F29: Database Schema

This merge request creates the required database schema. Fixes #37 (closed)

Checklist before merging

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

Further actions to consider

• All database fields are explained by a help text
• Check if a necessary fields are set before publishing an artwork
• The relation between an artwork and an exhibition is modeled using a ManyToManyField
• Integrate python-magic