F30: Adds an admin interface

This merge requests implements a fully functional administration interface using Django admin.

It depends on the database model provided by !18 (merged).

Fixes issues #41 (closed) Fixes issue #42 (closed)

Checklist before merging

• All functions contain type hints
• All functions are documented
• All functions are tested

Further actions to consider

• Add a button to quickly open a map pointing to the longitude and latitude of an artwork
• Split the admin models into their own files
• Convert https://youtu.be/[video-id] links to https://www.youtube.com/watch?v=[video-id] links