Remove CuratorRepository and AdminRepository

This gets rid of the custom repositories for contributors with special permissions, and adds the information to the contributor directly. The changes are straight-forward, but since it touches deleting of entities, a second opinion is welcome!

We discussed this a while back, and it would help with some other restructuring. The "downside" is that I had to remove two tests, because they would now require extra infrastructure to actually create the contributor in order to work. I tried to add that, but it introduces a lot of coupling for little gain, so I decided to delete those.