Resolve "Queries for current_{next,future} are still broken"

Closes #51

See merge request !140

Do release 2.2

See merge request AlekSIS/official/AlekSIS-App-Untis!137

Resolve "Import terms: Calling QuerySet.filter() after union() is not supported"

Closes #43

See merge request AlekSIS/official/AlekSIS-App-Untis!136

Bump version to 2.2a0

See merge request AlekSIS/official/AlekSIS-App-Untis!135

Resolve "Create match failures as data checks"

Closes #41

See merge request !120

Translations update from Weblate

See merge request AlekSIS/official/AlekSIS-App-Untis!125

Currently translated at 100.0% (28 of 28 strings)

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

Update translation files

See merge request AlekSIS/official/AlekSIS-App-Untis!132

Use new change tracker from Chronos

See merge request AlekSIS/official/AlekSIS-App-Untis!127

Resolve "Lesson periods are deleted and then cause data problems"

Closes #47

See merge request AlekSIS/official/AlekSIS-App-Untis!131

Resolve "Fuzzy matching of course groups"

Closes #46

See merge request AlekSIS/official/AlekSIS-App-Untis!129

Resolve "Take teachers into account when matching course groups"

Closes #45

See merge request AlekSIS/official/AlekSIS-App-Untis!128

Merge branch '45-take-teachers-into-account-when-matching-course-groups' into 46-fuzzy-matching-of-course-groups

Update dev dependencies

See merge request AlekSIS/official/AlekSIS-App-Untis!130

Release 2.1.3

See merge request AlekSIS/official/AlekSIS-App-Untis!126

Let management command default to current

See merge request AlekSIS/official/AlekSIS-App-Untis!124