Reduce backend dependencies on model layer via parametization (pt. 1)
Reduce backend dependencies on model layer via parametization (pt. 2)
Reduce backend dependencies on model layer via parametization (pt. 3)
Add missing groups param to (currently unused) login handler
Reduce backend dependencies on model layer via parametization (pt. 4)
Merge branch 'master' into backend_separation
Remove unused methods
Reduce backend dependencies on model layer via parametization (pt. 5)

For some parts of the backend API with need created items to have an ID
so we can report it to the event system. For this a new type constaint
called `WithId` has been added on `create()`-type methods. The `AnyModel`
trait inherits from `WithId`.
Backend cleanup and removal of unneeded classes
Merge branch 'master' into backend_separation

Conflicts:
	modules/core/app/backend/rest/AdminDAO.scala