Merge branch '79-filter-selects-on-week-overview-and-register-absence' into '73-add-rules-and-permissions'

Resolve "Filter selects on week overview and register absence"

See merge request !72

Merge branch '73-add-rules-and-permissions' into '79-filter-selects-on-week-overview-and-register-absence'

# Conflicts:
#   aleksis/apps/alsijil/forms.py

Resolve "Fix register absence form"

Closes #96

See merge request !84

Filter person dropdown list of absence registration form with custom queryset instead of queryset_rules_filter

Merge branch '73-add-rules-and-permissions' into 79-filter-selects-on-week-overview-and-register-absence

Resolve "Allow teachers opening lessons on the same day before they start"

Closes #95

See merge request !83

Save not only week, but year for week-related stuff

See merge request !82

Merge branch '64-make-it-possible-to-take-over-the-data-of-the-first-lesson-for-double-lessons' into 'master'

Resolve "Carry over the data of the first lesson for double (or triple, ...) lessons"

Closes #64

See merge request !79

Merge branch 'master' into 64-make-it-possible-to-take-over-the-data-of-the-first-lesson-for-double-lessons

Makes it possible to use the function in other contexts

Save groups a person is member of when personal notes are created

Closes #89

See merge request !78

Update dependency pytest to v6

See merge request !74

Fix #89 to fully work

Update dependency flake8-isort to v4

See merge request !77