Move djangoq settings to base settings

See merge request !222

Updating language menu

See merge request !223

Done to make djangoq settings accessible in production.
The sync setting is changed to the default False value since the run
order of the tasks is not relevant for our use case.
Mail sending functions have gotten a sync argument to force the tasks to
complete before checking their consequences in tests.

GREG-158: Better error reponse when e-mail sending failed for invite

See merge request !218

Change the permission classes for the core API

See merge request !221

GREG-156: Updating max date for role when user presses back button

See merge request !219

GREG-157: Changing background colour of link section to create more contrast with text colour

See merge request !220

- Set the default to IsAdminUser
- Set it explicitly on all the views
- Add tests

Translate files spellchecking

See merge request !217

Show all ous sponsor can access in register form

See merge request !214

Reduce use of red in styling

See merge request !216

Removing duplicate entry

See merge request !213

Overview buttons now have black text. Sponsor menu arrows are now black.
Links in footer has white underline on hover, otherwise nothing.

Resolves: GREG-15

Add CSRF_TRUSTED_ORIGINS to development settings

See merge request !215

Bump dependencies

See merge request !211

Adding missing gender to person API output

See merge request !212

Notable upgrades:
- Django from 3.2.9 to 4.0
- djangorestframework from 3.12.4 to 3.13.0