Resolve "Frontend for Models"

Closes #1 (closed)

aleksis/apps/lesrooster/frontend/messages/en.json

+{
+  "lesrooster": {
+    "menu_title": "Lesson Management",
+    "validity_range": {
+      "menu_title": "Validity Ranges",
+      "title": "Validity Range",
+      "title_plural": "Validity Ranges",
+      "name": "Name",
+      "date_start": "Start Date",
+      "date_end": "End Date",
+      "create_validity_range": "Create Validity Range"
+    },
+    "slot": {
+      "menu_title": "Slots",
+      "title": "Slot",
+      "title_plural": "Slots",
+      "name": "Name",
+      "weekday": "Weekday",
+      "period": "Period",
+      "time_start": "Start Time",
+      "time_end": "End Time",
+      "create_slot": "Create Slot"
+    },
+    "break": {
+      "menu_title": "Breaks",
+      "title": "Break",
+      "title_plural": "Break",
+      "create_item": "Create Break"
+    }
+  }
+}
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