Resolve "URL "lesson" does not exist and thus can't be resolved"

Closes #144

See merge request !150

Update poetry.lock

See merge request !151

Resolve "Extra marks and custom excuses (potentially) counted multiple times"

Closes #142

See merge request !148

Merge branch '135-week-view-get-holidays-by-actual-weekday-and-not-by-for-loop-counter' into 'master'

Resolve "[Week view] Get holidays by actual weekday and not by for loop counter"

Closes #135

See merge request !147

Fix typo

See merge request !149

Resolve "Negative values for tardiness are not rejected"

Closes #141

See merge request !146

Closes #141

Resolve "is_none predicate is actually is_not_none"

Closes #140

See merge request !145

Translations update from Weblate

See merge request !144

Currently translated at 100.0% (236 of 236 strings)

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

Currently translated at 100.0% (236 of 236 strings)

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

Currently translated at 100.0% (236 of 236 strings)

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

Currently translated at 100.0% (236 of 236 strings)

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

Update translation files

See merge request !143

Resolve "Support events and extra lessons in class register"

Closes #71

See merge request !120