Upgrade to DSC 3.0

[tymees]

The future is here! We'll need to upgrade to this future at some point.

In general, the migration guide can be used: https://dh-it-portal-development.github.io/django-shared-core/

However, for this app there are some extra things to do/consider:

• Adding Django Impersonate (#60)
• It's recommended to upgrade to Django 4.0 as well
• Introducing an 'app' color; this is something Ben and I talked about, to better differentiate our apps. The idea that every app should use one color as it's main highlight.

I can't assign to multiple people, so I'm just gonna namedrop: @maartenuni @bbonf

[bbonf]

Fixed in #68 right?

[tymees]

Jup