Translations update from Weblate

See merge request !225

Resolve "Automatic plan update fails because of missing version object"

Closes #159

See merge request !223

Currently translated at 100.0% (135 of 135 strings)

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

Update translation files

See merge request !226

Drop poetry.lock

See merge request !224

Fix readme reference

See merge request !222

Resolve "Names of subjects should not have to be unique"

Closes #158

See merge request !221

[Fixtures] Fix number and period of validity ranges

See merge request !220

Remove admin user from test data

See merge request !219

Add trademark hint to readme

See merge request !218

Resolve "Allow editing of subject field on Group model in frontend"

Closes #156

See merge request !215

Resolve "Announcements are not shown on substitutions printout"

Closes #157

See merge request !216

Update dev dependencies and reformat

See merge request !217

Merge branch '155-automaticplan-doesn-t-look-at-versions-between-the-last-revision-and-the-current-revision' into 'master'

Resolve "AutomaticPlan doesn't look at versions between the last revision and the current revision"

Closes #155

See merge request !214

Add makemessages env to tox.ini

See merge request !213

Merge branch '154-nameerror-at-app-resint-live_documents-pdf-name-timedelta-is-not-defined' into 'master'

Resolve "NameError at /app/resint/live_documents/*.pdf: name 'timedelta' is not defined"

Closes #154

See merge request AlekSIS/official/AlekSIS-App-Chronos!212

Bump version to 2.1.dev0

See merge request !211