[FEATURE] new rest api

__Tasks:__
- [x] refactor all controllers to new api
- [ ] gather feedback for my changes 

__Informations:__

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| Tests pass?   | none
| Fixed tickets | [none]
| Doc           | none
@marcelmoosbrugger I would not separate create and get in this case, especially if we want to add the language later. Just use the getFieldDescriptors and save the return value in the controller, in case you need it often.