[FEATURE] REST API Refactoring

replaces #120 

- [x] refactor the REST-Controllers to meet new API requirements
- [ ] gather feedback for my changes

__Informations:__

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| Tests pass?   | no the PUTs fail
| Fixed tickets | none
| Doc           | none

__Requires:__
- https://github.com/sulu-cmf/SuluContactBundle/pull/113
@l91 uses constants for this in the `MediaManager` I think