Resolve "Importing exams broken due to missing time period"

Closes #57

See merge request !159

Drop support for GitHub

See merge request !158

Undo wrong change in absence importer

See merge request !157

Release 2.3.2

See merge request !156

Merge branch '53-guess_school_id-migration-does-not-work-properly-coming-from-untis-2-1-3' into 'master'

Resolve "guess_school_id migration does not work properly coming from Untis 2.1.3"

Closes #53

See merge request !155

Resolve "Use teachers only as fallback for course group matching"

Closes #56

See merge request !154

Do release 2.3.1

See merge request !152

Fix two bugs with importing lessons

Closes #54 and #55

See merge request !151

Translations update from Weblate

See merge request !149

Currently translated at 100.0% (38 of 38 strings)

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

Currently translated at 100.0% (38 of 38 strings)

Translation: AlekSIS/AlekSIS-App-Untis
Translate-URL: https://translate.edugit.org/projects/aleksis/aleksis-app-untis/ru/

Do release 2.3

See merge request !148

Translations update from Weblate

See merge request !143

Currently translated at 100.0% (36 of 36 strings)

Translation: AlekSIS/AlekSIS-App-Untis
Translate-URL: https://translate.edugit.org/projects/aleksis/aleksis-app-untis/ru/

Currently translated at 100.0% (36 of 36 strings)

Translation: AlekSIS/AlekSIS-App-Untis
Translate-URL: https://translate.edugit.org/projects/aleksis/aleksis-app-untis/ru/

Currently translated at 100.0% (36 of 36 strings)

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

Currently translated at 75.0% (27 of 36 strings)

Translation: AlekSIS/AlekSIS-App-Untis
Translate-URL: https://translate.edugit.org/projects/aleksis/aleksis-app-untis/ru/

Update translation files

See merge request !147

Resolve "Import exams/announcement from calendar via MySQL"

Closes #5

See merge request !146