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

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

Closes #872

See merge request !1271

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

Translations update from Weblate

See merge request !1219

Translations update from Weblate

See merge request !1240

Currently translated at 84.7% (133 of 157 strings)

Translation: AlekSIS/AlekSIS-Core-Frontend
Translate-URL: https://translate.edugit.org/projects/aleksis/aleksis-core-frontend/ru/

Currently translated at 100.0% (157 of 157 strings)

Translation: AlekSIS/AlekSIS-Core-Frontend
Translate-URL: https://translate.edugit.org/projects/aleksis/aleksis-core-frontend/uk/

Resolve "Urls in confimation email contains the /django/ prefix"

Closes #852

See merge request !1253

Resolve "Improve performance of polling queries"

Closes #847

See merge request !1252

Resolve "Fix whoAmI query" (and make permission query poll)

Closes #860

See merge request !1250

Resolve "Doc for maintainance tasks still mentions yarn install"

Closes #861

See merge request !1251

Merge branch '856-language-select-uses-english-as-default-language-and-not-browser-language' into 'master'

Resolve "Language select uses English as default language (and not browser language)"

Closes #856

See merge request !1245

Merge branch 'master' into '856-language-select-uses-english-as-default-language-and-not-browser-language'

# Conflicts:
#   CHANGELOG.rst