Update dev dependencies and reformat

See merge request !98

Resolve "Classes without teachers break import"

Closes #32

See merge request !97

Add makemessages env to tox.ini

See merge request !96

Bump development version to 2.1.dev0

See merge request !95

Update changelog from 2.0

See merge request !94

(cherry picked from commit 69336497)

Resolve "Management commands are not run in the frontend"

Closes #29

See merge request !91

Update poetry.lock

See merge request !92

Provide demo data

See merge request !90

Update changelog from 2.0rc3

See merge request !89

(cherry picked from commit 9778e774)

Resolve "Assign rooms correctly"

Closes #27

See merge request !84

Resolve "Skip extra lessons without a subject"

Closes #28

See merge request !87

Update poetry.lock

See merge request !86

Update poetry.lock

See merge request !85

Update changelog from 2.0rc2

See merge request !83

(cherry picked from commit 7915b78d)

Merge branch '26-validity-ranges-are-linked-to-terms-only-by-untis-id-and-not-by-school-term' into 'master'

Resolve "Validity ranges are linked to terms only by Untis ID and not by school term"

Closes #26

See merge request !81

Wrap the complete import in an atomic revision

See merge request !80

Update poetry.lock

See merge request !79