diff --git a/biscuit/apps/chronos/locale/ar/LC_MESSAGES/django.po b/biscuit/apps/chronos/locale/ar/LC_MESSAGES/django.po
index 5ededc43d53a0941442dcb80506d735ddd0afe80..900e44f841517baad5bc7b9f4efffb516522f856 100644
--- a/biscuit/apps/chronos/locale/ar/LC_MESSAGES/django.po
+++ b/biscuit/apps/chronos/locale/ar/LC_MESSAGES/django.po
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2019-09-17 23:02+0200\n"
+"POT-Creation-Date: 2019-11-03 20:10+0100\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -27,7 +27,7 @@ msgstr ""
 msgid "Teacher"
 msgstr ""
 
-#: forms.py:21 models.py:129
+#: forms.py:21 models.py:257
 msgid "Room"
 msgstr ""
 
@@ -35,7 +35,7 @@ msgstr ""
 msgid "Timetables"
 msgstr ""
 
-#: menus.py:12 templates/chronos/tt_week.html:11 views.py:94
+#: menus.py:12 templates/chronos/tt_week.html:11 views.py:76
 msgid "Timetable"
 msgstr ""
 
@@ -43,91 +43,91 @@ msgstr ""
 msgid "Daily lessons"
 msgstr ""
 
-#: models.py:17
+#: models.py:145
 msgid "Sunday"
 msgstr ""
 
-#: models.py:18
+#: models.py:146
 msgid "Monday"
 msgstr ""
 
-#: models.py:19
+#: models.py:147
 msgid "Tuesday"
 msgstr ""
 
-#: models.py:20
+#: models.py:148
 msgid "Wednesday"
 msgstr ""
 
-#: models.py:21
+#: models.py:149
 msgid "Thursday"
 msgstr ""
 
-#: models.py:22
+#: models.py:150
 msgid "Friday"
 msgstr ""
 
-#: models.py:23
+#: models.py:151
 msgid "Saturday"
 msgstr ""
 
-#: models.py:27
+#: models.py:155
 msgid "Week day"
 msgstr ""
 
-#: models.py:29
+#: models.py:157
 msgid "Number of period"
 msgstr ""
 
-#: models.py:31
+#: models.py:159
 msgid "Time the period starts"
 msgstr ""
 
-#: models.py:32
+#: models.py:160
 msgid "Time the period ends"
 msgstr ""
 
-#: models.py:53
+#: models.py:181
 msgid "Abbreviation of subject in timetable"
 msgstr ""
 
-#: models.py:55
+#: models.py:183
 msgid "Long name of subject"
 msgstr ""
 
-#: models.py:57
+#: models.py:185
 msgid "Foreground colour in timetable"
 msgstr ""
 
-#: models.py:59
+#: models.py:187
 msgid "Background colour in timetable"
 msgstr ""
 
-#: models.py:72
+#: models.py:200
 msgid "Short name, e.g. room number"
 msgstr ""
 
-#: models.py:73
+#: models.py:201
 msgid "Long name"
 msgstr ""
 
-#: models.py:93
+#: models.py:221
 msgid "Effective start date of lesson"
 msgstr ""
 
-#: models.py:95
+#: models.py:223
 msgid "Effective end date of lesson"
 msgstr ""
 
-#: models.py:118
+#: models.py:246
 msgid "Week"
 msgstr ""
 
-#: models.py:126
+#: models.py:254
 msgid "Subject"
 msgstr ""
 
-#: models.py:135
+#: models.py:263
 msgid "Lessons can only be either substituted or cancelled."
 msgstr ""
 
@@ -172,15 +172,15 @@ msgstr ""
 msgid "to"
 msgstr ""
 
-#: views.py:130
+#: views.py:107
 #, python-format
 msgid "Lessons %s"
 msgstr ""
 
-#: views.py:166
+#: views.py:142
 msgid "The substitution has been saved."
 msgstr ""
 
-#: views.py:185
+#: views.py:161
 msgid "The substitution has been deleted."
 msgstr ""
diff --git a/biscuit/apps/chronos/locale/de_DE/LC_MESSAGES/django.po b/biscuit/apps/chronos/locale/de_DE/LC_MESSAGES/django.po
index 3c2b0e163bd387c11be3b7301ba61a1e598ac32d..22f657808a01e2967b3da7ed3b78eb1a26297e48 100644
--- a/biscuit/apps/chronos/locale/de_DE/LC_MESSAGES/django.po
+++ b/biscuit/apps/chronos/locale/de_DE/LC_MESSAGES/django.po
@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: \n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2019-09-17 23:02+0200\n"
+"POT-Creation-Date: 2019-11-03 20:10+0100\n"
 "PO-Revision-Date: 2019-09-17 21:08+0000\n"
 "Last-Translator: Tom Teichler <tom.teichler@teckids.org>\n"
 "Language-Team: German <https://translate.edugit.org/projects/biscuit-sis/"
@@ -27,7 +27,7 @@ msgstr "Gruppe"
 msgid "Teacher"
 msgstr "Lehrkraft"
 
-#: forms.py:21 models.py:129
+#: forms.py:21 models.py:257
 msgid "Room"
 msgstr "Raum"
 
@@ -35,7 +35,7 @@ msgstr "Raum"
 msgid "Timetables"
 msgstr "Stundenpläne"
 
-#: menus.py:12 templates/chronos/tt_week.html:11 views.py:94
+#: menus.py:12 templates/chronos/tt_week.html:11 views.py:76
 msgid "Timetable"
 msgstr "Stundenplan"
 
@@ -43,91 +43,91 @@ msgstr "Stundenplan"
 msgid "Daily lessons"
 msgstr "Tages-Stunden"
 
-#: models.py:17
+#: models.py:145
 msgid "Sunday"
 msgstr "Sonntag"
 
-#: models.py:18
+#: models.py:146
 msgid "Monday"
 msgstr "Montag"
 
-#: models.py:19
+#: models.py:147
 msgid "Tuesday"
 msgstr "Dienstag"
 
-#: models.py:20
+#: models.py:148
 msgid "Wednesday"
 msgstr "Mittwoch"
 
-#: models.py:21
+#: models.py:149
 msgid "Thursday"
 msgstr "Donnerstag"
 
-#: models.py:22
+#: models.py:150
 msgid "Friday"
 msgstr "Freitag"
 
-#: models.py:23
+#: models.py:151
 msgid "Saturday"
 msgstr "Samstag"
 
-#: models.py:27
+#: models.py:155
 msgid "Week day"
 msgstr "Wochentag"
 
-#: models.py:29
+#: models.py:157
 msgid "Number of period"
 msgstr "Nummer der Stunde"
 
-#: models.py:31
+#: models.py:159
 msgid "Time the period starts"
 msgstr "Anfangszeit der Stunde"
 
-#: models.py:32
+#: models.py:160
 msgid "Time the period ends"
 msgstr "Endzeit der Stunde"
 
-#: models.py:53
+#: models.py:181
 msgid "Abbreviation of subject in timetable"
 msgstr "Kürzel des Faches im Stundenplan"
 
-#: models.py:55
+#: models.py:183
 msgid "Long name of subject"
 msgstr "Name des Faches"
 
-#: models.py:57
+#: models.py:185
 msgid "Foreground colour in timetable"
 msgstr "Vordergrundfarbe im Stundenplan"
 
-#: models.py:59
+#: models.py:187
 msgid "Background colour in timetable"
 msgstr "Hintergrundfarbe im Stundenplan"
 
-#: models.py:72
+#: models.py:200
 msgid "Short name, e.g. room number"
 msgstr "Kurzer Name, z.B. Raumnummer"
 
-#: models.py:73
+#: models.py:201
 msgid "Long name"
 msgstr "Langer Name"
 
-#: models.py:93
+#: models.py:221
 msgid "Effective start date of lesson"
 msgstr "Effektives Startdatum des Unterrichts"
 
-#: models.py:95
+#: models.py:223
 msgid "Effective end date of lesson"
 msgstr "Effektives Enddatum des Unterrichts"
 
-#: models.py:118
+#: models.py:246
 msgid "Week"
 msgstr "Woche"
 
-#: models.py:126
+#: models.py:254
 msgid "Subject"
 msgstr "Fach"
 
-#: models.py:135
+#: models.py:263
 msgid "Lessons can only be either substituted or cancelled."
 msgstr ""
 "Unterrichtsstunden können nur entweder vertreten werden oder ausfallen."
@@ -173,16 +173,16 @@ msgstr "Kalenderwoche"
 msgid "to"
 msgstr "bis"
 
-#: views.py:130
+#: views.py:107
 #, python-format
 msgid "Lessons %s"
 msgstr "Unterrichtsstunden %s"
 
-#: views.py:166
+#: views.py:142
 msgid "The substitution has been saved."
 msgstr "Die Vertretung wurde gespeichert."
 
-#: views.py:185
+#: views.py:161
 msgid "The substitution has been deleted."
 msgstr "Die Vertretung wurde gelöscht."
 
diff --git a/biscuit/apps/chronos/locale/fr/LC_MESSAGES/django.po b/biscuit/apps/chronos/locale/fr/LC_MESSAGES/django.po
index 48076cd8980c90746c373cf8d40db9a30f8a2cc0..b789ca41471346ee9231d148eb2caef88e92e6ed 100644
--- a/biscuit/apps/chronos/locale/fr/LC_MESSAGES/django.po
+++ b/biscuit/apps/chronos/locale/fr/LC_MESSAGES/django.po
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2019-09-17 23:02+0200\n"
+"POT-Creation-Date: 2019-11-03 20:10+0100\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -26,7 +26,7 @@ msgstr ""
 msgid "Teacher"
 msgstr ""
 
-#: forms.py:21 models.py:129
+#: forms.py:21 models.py:257
 msgid "Room"
 msgstr ""
 
@@ -34,7 +34,7 @@ msgstr ""
 msgid "Timetables"
 msgstr ""
 
-#: menus.py:12 templates/chronos/tt_week.html:11 views.py:94
+#: menus.py:12 templates/chronos/tt_week.html:11 views.py:76
 msgid "Timetable"
 msgstr ""
 
@@ -42,91 +42,91 @@ msgstr ""
 msgid "Daily lessons"
 msgstr ""
 
-#: models.py:17
+#: models.py:145
 msgid "Sunday"
 msgstr ""
 
-#: models.py:18
+#: models.py:146
 msgid "Monday"
 msgstr ""
 
-#: models.py:19
+#: models.py:147
 msgid "Tuesday"
 msgstr ""
 
-#: models.py:20
+#: models.py:148
 msgid "Wednesday"
 msgstr ""
 
-#: models.py:21
+#: models.py:149
 msgid "Thursday"
 msgstr ""
 
-#: models.py:22
+#: models.py:150
 msgid "Friday"
 msgstr ""
 
-#: models.py:23
+#: models.py:151
 msgid "Saturday"
 msgstr ""
 
-#: models.py:27
+#: models.py:155
 msgid "Week day"
 msgstr ""
 
-#: models.py:29
+#: models.py:157
 msgid "Number of period"
 msgstr ""
 
-#: models.py:31
+#: models.py:159
 msgid "Time the period starts"
 msgstr ""
 
-#: models.py:32
+#: models.py:160
 msgid "Time the period ends"
 msgstr ""
 
-#: models.py:53
+#: models.py:181
 msgid "Abbreviation of subject in timetable"
 msgstr ""
 
-#: models.py:55
+#: models.py:183
 msgid "Long name of subject"
 msgstr ""
 
-#: models.py:57
+#: models.py:185
 msgid "Foreground colour in timetable"
 msgstr ""
 
-#: models.py:59
+#: models.py:187
 msgid "Background colour in timetable"
 msgstr ""
 
-#: models.py:72
+#: models.py:200
 msgid "Short name, e.g. room number"
 msgstr ""
 
-#: models.py:73
+#: models.py:201
 msgid "Long name"
 msgstr ""
 
-#: models.py:93
+#: models.py:221
 msgid "Effective start date of lesson"
 msgstr ""
 
-#: models.py:95
+#: models.py:223
 msgid "Effective end date of lesson"
 msgstr ""
 
-#: models.py:118
+#: models.py:246
 msgid "Week"
 msgstr ""
 
-#: models.py:126
+#: models.py:254
 msgid "Subject"
 msgstr ""
 
-#: models.py:135
+#: models.py:263
 msgid "Lessons can only be either substituted or cancelled."
 msgstr ""
 
@@ -171,15 +171,15 @@ msgstr ""
 msgid "to"
 msgstr ""
 
-#: views.py:130
+#: views.py:107
 #, python-format
 msgid "Lessons %s"
 msgstr ""
 
-#: views.py:166
+#: views.py:142
 msgid "The substitution has been saved."
 msgstr ""
 
-#: views.py:185
+#: views.py:161
 msgid "The substitution has been deleted."
 msgstr ""
diff --git a/biscuit/apps/chronos/locale/nb_NO/LC_MESSAGES/django.po b/biscuit/apps/chronos/locale/nb_NO/LC_MESSAGES/django.po
index 386838f9c720399ecaaff42b5b26837b7efc7b49..7fb6adb6518963f3b112c439782a7ad173618623 100644
--- a/biscuit/apps/chronos/locale/nb_NO/LC_MESSAGES/django.po
+++ b/biscuit/apps/chronos/locale/nb_NO/LC_MESSAGES/django.po
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2019-09-17 23:02+0200\n"
+"POT-Creation-Date: 2019-11-03 20:10+0100\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -25,7 +25,7 @@ msgstr ""
 msgid "Teacher"
 msgstr ""
 
-#: forms.py:21 models.py:129
+#: forms.py:21 models.py:257
 msgid "Room"
 msgstr ""
 
@@ -33,7 +33,7 @@ msgstr ""
 msgid "Timetables"
 msgstr ""
 
-#: menus.py:12 templates/chronos/tt_week.html:11 views.py:94
+#: menus.py:12 templates/chronos/tt_week.html:11 views.py:76
 msgid "Timetable"
 msgstr ""
 
@@ -41,91 +41,91 @@ msgstr ""
 msgid "Daily lessons"
 msgstr ""
 
-#: models.py:17
+#: models.py:145
 msgid "Sunday"
 msgstr ""
 
-#: models.py:18
+#: models.py:146
 msgid "Monday"
 msgstr ""
 
-#: models.py:19
+#: models.py:147
 msgid "Tuesday"
 msgstr ""
 
-#: models.py:20
+#: models.py:148
 msgid "Wednesday"
 msgstr ""
 
-#: models.py:21
+#: models.py:149
 msgid "Thursday"
 msgstr ""
 
-#: models.py:22
+#: models.py:150
 msgid "Friday"
 msgstr ""
 
-#: models.py:23
+#: models.py:151
 msgid "Saturday"
 msgstr ""
 
-#: models.py:27
+#: models.py:155
 msgid "Week day"
 msgstr ""
 
-#: models.py:29
+#: models.py:157
 msgid "Number of period"
 msgstr ""
 
-#: models.py:31
+#: models.py:159
 msgid "Time the period starts"
 msgstr ""
 
-#: models.py:32
+#: models.py:160
 msgid "Time the period ends"
 msgstr ""
 
-#: models.py:53
+#: models.py:181
 msgid "Abbreviation of subject in timetable"
 msgstr ""
 
-#: models.py:55
+#: models.py:183
 msgid "Long name of subject"
 msgstr ""
 
-#: models.py:57
+#: models.py:185
 msgid "Foreground colour in timetable"
 msgstr ""
 
-#: models.py:59
+#: models.py:187
 msgid "Background colour in timetable"
 msgstr ""
 
-#: models.py:72
+#: models.py:200
 msgid "Short name, e.g. room number"
 msgstr ""
 
-#: models.py:73
+#: models.py:201
 msgid "Long name"
 msgstr ""
 
-#: models.py:93
+#: models.py:221
 msgid "Effective start date of lesson"
 msgstr ""
 
-#: models.py:95
+#: models.py:223
 msgid "Effective end date of lesson"
 msgstr ""
 
-#: models.py:118
+#: models.py:246
 msgid "Week"
 msgstr ""
 
-#: models.py:126
+#: models.py:254
 msgid "Subject"
 msgstr ""
 
-#: models.py:135
+#: models.py:263
 msgid "Lessons can only be either substituted or cancelled."
 msgstr ""
 
@@ -170,15 +170,15 @@ msgstr ""
 msgid "to"
 msgstr ""
 
-#: views.py:130
+#: views.py:107
 #, python-format
 msgid "Lessons %s"
 msgstr ""
 
-#: views.py:166
+#: views.py:142
 msgid "The substitution has been saved."
 msgstr ""
 
-#: views.py:185
+#: views.py:161
 msgid "The substitution has been deleted."
 msgstr ""
diff --git a/biscuit/apps/chronos/locale/tr_TR/LC_MESSAGES/django.po b/biscuit/apps/chronos/locale/tr_TR/LC_MESSAGES/django.po
index 386838f9c720399ecaaff42b5b26837b7efc7b49..7fb6adb6518963f3b112c439782a7ad173618623 100644
--- a/biscuit/apps/chronos/locale/tr_TR/LC_MESSAGES/django.po
+++ b/biscuit/apps/chronos/locale/tr_TR/LC_MESSAGES/django.po
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2019-09-17 23:02+0200\n"
+"POT-Creation-Date: 2019-11-03 20:10+0100\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -25,7 +25,7 @@ msgstr ""
 msgid "Teacher"
 msgstr ""
 
-#: forms.py:21 models.py:129
+#: forms.py:21 models.py:257
 msgid "Room"
 msgstr ""
 
@@ -33,7 +33,7 @@ msgstr ""
 msgid "Timetables"
 msgstr ""
 
-#: menus.py:12 templates/chronos/tt_week.html:11 views.py:94
+#: menus.py:12 templates/chronos/tt_week.html:11 views.py:76
 msgid "Timetable"
 msgstr ""
 
@@ -41,91 +41,91 @@ msgstr ""
 msgid "Daily lessons"
 msgstr ""
 
-#: models.py:17
+#: models.py:145
 msgid "Sunday"
 msgstr ""
 
-#: models.py:18
+#: models.py:146
 msgid "Monday"
 msgstr ""
 
-#: models.py:19
+#: models.py:147
 msgid "Tuesday"
 msgstr ""
 
-#: models.py:20
+#: models.py:148
 msgid "Wednesday"
 msgstr ""
 
-#: models.py:21
+#: models.py:149
 msgid "Thursday"
 msgstr ""
 
-#: models.py:22
+#: models.py:150
 msgid "Friday"
 msgstr ""
 
-#: models.py:23
+#: models.py:151
 msgid "Saturday"
 msgstr ""
 
-#: models.py:27
+#: models.py:155
 msgid "Week day"
 msgstr ""
 
-#: models.py:29
+#: models.py:157
 msgid "Number of period"
 msgstr ""
 
-#: models.py:31
+#: models.py:159
 msgid "Time the period starts"
 msgstr ""
 
-#: models.py:32
+#: models.py:160
 msgid "Time the period ends"
 msgstr ""
 
-#: models.py:53
+#: models.py:181
 msgid "Abbreviation of subject in timetable"
 msgstr ""
 
-#: models.py:55
+#: models.py:183
 msgid "Long name of subject"
 msgstr ""
 
-#: models.py:57
+#: models.py:185
 msgid "Foreground colour in timetable"
 msgstr ""
 
-#: models.py:59
+#: models.py:187
 msgid "Background colour in timetable"
 msgstr ""
 
-#: models.py:72
+#: models.py:200
 msgid "Short name, e.g. room number"
 msgstr ""
 
-#: models.py:73
+#: models.py:201
 msgid "Long name"
 msgstr ""
 
-#: models.py:93
+#: models.py:221
 msgid "Effective start date of lesson"
 msgstr ""
 
-#: models.py:95
+#: models.py:223
 msgid "Effective end date of lesson"
 msgstr ""
 
-#: models.py:118
+#: models.py:246
 msgid "Week"
 msgstr ""
 
-#: models.py:126
+#: models.py:254
 msgid "Subject"
 msgstr ""
 
-#: models.py:135
+#: models.py:263
 msgid "Lessons can only be either substituted or cancelled."
 msgstr ""
 
@@ -170,15 +170,15 @@ msgstr ""
 msgid "to"
 msgstr ""
 
-#: views.py:130
+#: views.py:107
 #, python-format
 msgid "Lessons %s"
 msgstr ""
 
-#: views.py:166
+#: views.py:142
 msgid "The substitution has been saved."
 msgstr ""
 
-#: views.py:185
+#: views.py:161
 msgid "The substitution has been deleted."
 msgstr ""