Add preference to enable/disable dashboard editing

Closes #395

See merge request !507

Resolve "Add dashboard widget for external link"

Closes #383

See merge request !505

Resolve "Support default dashboard for anonymous users"

Closes #382

See merge request !506

Resolve "Problems with dirty fields tracker while using (get_or_)create"

Closes #392

See merge request !503

Update Django dependency

See merge request !504

Closes #392

Remove duplicate definition of extra_data field.

See merge request !499

[DjDT] Disable redirects panel

See merge request !498

Resolve "Add health check for dbbackup"

Closes #378

See merge request !495

Translations update from Weblate

See merge request !496

Currently translated at 100.0% (439 of 439 strings)

Translation: AlekSIS/AlekSIS-Core
Translate-URL: https://translate.edugit.org/projects/aleksis/aleksis/de/

Resolve "Make Celery non-optional"

Closes #359

See merge request !491

This reverts commit c82be665.

This reverts commit 3bae1a9a.

Retrospectively, there is no reasonto wrap every request in a
transaction of its own. Developer should actively consider isolation
in their code.

This came up while trying to figure out how to delay every Celery task
until commit, finding us monkey-patching amqp, and failing.

Merge branch '359-make-celery-non-optional' of edugit.org:AlekSIS/Official/AlekSIS-Core into 359-make-celery-non-optional

Merge branch '359-make-celery-non-optional' of edugit.org:AlekSIS/official/AlekSIS-Core into 359-make-celery-non-optional