Review data model again

[lislis]

Considering usage of https://github.com/paper-trail-gem/paper_trail
Does anything make sense anymore?
Looking especially at how settings can be used to describe the structure of case data and then how we render case data via a nice endpoint and the magic that needs to happen in between

[lislis]

• is Attribute necessary? Can it be only Category on Entity?

[lislis]

• remove Change in favor of papertrail https://github.com/paper-trail-gem/paper_trail
• Write documentation to explain how models fit together. With diagrams and examples!

[lislis]

• refactor Attribute such that:
  • Entity has_many Attributes
  • Attribute is either Field, YesNo or Category (where YesNo also includes Field in the end if yes is selected)
  • these changes need to be reflected in the frontend of the data schema settings