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 !212

Bump version to 2.1.dev0

See merge request AlekSIS/official/AlekSIS-App-Chronos!211

Resolve "Automatically create a PDF file of the substitution plan"

Closes #116

See merge request !191

Resolve "Events replace lessons"

Closes #127

See merge request !207

Update changelog from 2.0

See merge request !210

(cherry picked from commit 3dd7f9f3)

Fix changelog order

See merge request !208

Resolve "Improve the formatting of the substitution plan"

Closes #152

See merge request !206

Merge local master to new empty branch

Resolve "Substitution is shown on regular/print timetable"

Closes #149

See merge request !205

Provide fixtures for testing/demo instances

See merge request !204

Update poetry.lock

See merge request !203

Update changelog from 2.0rc3

See merge request !202

(cherry picked from commit e07e0794)