Prepare release 2.1.1

See merge request !118

Resolve "Allow selecting plan version and default to newest version"

Closes #40

See merge request !117

[Docs] Enable build

See merge request !115

Prepare release 2.1

See merge request !114

[Docs] Fix intersphinx mapping

See merge request !113

Translations update from Weblate

See merge request !112

Currently translated at 92.0% (23 of 25 strings)

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

Update translation files

See merge request !111

[Docs] Add references

See merge request !110

Add docs

See merge request !109

Resolve "Celery tasks are not working properly"

Closes #37

See merge request !108

Do not include non-package files in wheel

See merge request !107

Fix readme reference

See merge request !106

Resolve "Allow configuring database options"

Closes #36

See merge request !104

Resolve "Disambiguate long group names"

Closes #35

See merge request !103