Idea: refactor categories to build on the theory of wild categories

[fredrik-bakke]

This seems appropriate following the discussion with Anders after #910 that "properties", of categories should be separated from its "data", and allows us to repeat fewer arguments.

[EgbertRijke]

It is not yet clear to me that data should be separated from properties, as is implied, but we can definitely discuss this idea further.

[fredrik-bakke]

Oh, yes, I am not yet convinced by this idea either; I should have phrased the issue text differently. I still think this refactoring makes a lot of sense, though.