Resolve "Frontend issues after update to AlekSIS-Core 3.1.1"

Closes #873

See merge request !1276

Release 3.1.1

See merge request !1274

Create migration for newer version of django-oauth-toolkit

See merge request !1266

# Conflicts:
#   CHANGELOG.rst

Resolve "Some fields on person schema did not accept returning null values"

Closes #862

See merge request !1260

# Conflicts:
#   CHANGELOG.rst

Merge branch '866-scrolling-on-vuetify-based-pages-is-not-possible-when-the-celeryprogressbottom-drawer-is-open' into 'master'

Resolve "Scrolling on Vuetify-based pages is not possible when the CeleryProgressBottom drawer is open"

Closes #866

See merge request !1262

Merge branch 'master' into '866-scrolling-on-vuetify-based-pages-is-not-possible-when-the-celeryprogressbottom-drawer-is-open'

# Conflicts:
#   CHANGELOG.rst

Resolve "GraphQL error "DummyPerson needs a primary key""

Closes #865

See merge request !1254

# Conflicts:
#   CHANGELOG.rst

Merge branch '867-unreadnotificationscount-is-queried-when-accessing-notifications-even-though-there-is-no-need' into 'master'

Resolve "unreadNotificationsCount is queried when accessing notifications even though there is no need for it"

Closes #867

See merge request !1255

Merge branch 'master' into '867-unreadnotificationscount-is-queried-when-accessing-notifications-even-though-there-is-no-need'

# Conflicts:
#   CHANGELOG.rst

Merge branch '864-loading-bar-does-not-disappear-on-person-overview-pages-even-though-the-query-has-finished' into 'master'

Resolve "Loading bar does not disappear on person overview pages even though the query has finished"

Closes #864

See merge request !1256

# Conflicts:
#   CHANGELOG.rst

Resolve "About page fails to load if app with unkown licence is installed"

Closes #872

See merge request !1271

# Conflicts:
#   CHANGELOG.rst

Correctly save task status

See merge request !1267

Update dependency django-colorfield to ^0.9.0

See merge request !1263

Prepare release 3.1

See merge request !1264