Optimize exam models for importing exams from Untis

See merge request !257

Update changelog (add Ukrainian)

See merge request !256

Translations update from Weblate

See merge request !249

Currently translated at 100.0% (159 of 159 strings)

Translation: AlekSIS/AlekSIS-App-Chronos
Translate-URL: https://translate.edugit.org/projects/aleksis/aleksis-app-chronos/uk/

Currently translated at 100.0% (159 of 159 strings)

Translation: AlekSIS/AlekSIS-App-Chronos
Translate-URL: https://translate.edugit.org/projects/aleksis/aleksis-app-chronos/uk/

Currently translated at 13.8% (22 of 159 strings)

Translation: AlekSIS/AlekSIS-App-Chronos
Translate-URL: https://translate.edugit.org/projects/aleksis/aleksis-app-chronos/uk/

Currently translated at 11.9% (19 of 159 strings)

Translation: AlekSIS/AlekSIS-App-Chronos
Translate-URL: https://translate.edugit.org/projects/aleksis/aleksis-app-chronos/uk/

Currently translated at 4.4% (7 of 159 strings)

Translation: AlekSIS/AlekSIS-App-Chronos
Translate-URL: https://translate.edugit.org/projects/aleksis/aleksis-app-chronos/uk/

makemessages: Add support for Ukrainian and Russian.

See merge request !254

Resolve "Drop update() from AutomaticPlan"

Closes #163

See merge request !252

Resolve "Remove template folder `automatic_plan`"

Closes #172

See merge request !251

Resolve "Use iconify for Material Icons instead of icon font"

Closes #170

See merge request !250

Do release 2.3

See merge request !248

Translations update from Weblate

See merge request !239

Currently translated at 100.0% (161 of 161 strings)

Translation: AlekSIS/AlekSIS-App-Chronos
Translate-URL: https://translate.edugit.org/projects/aleksis/aleksis-app-chronos/de/

Update translation files

See merge request !247

Resolve "Notification for changes in the substitution plan"

Closes #50

See merge request !242