[ENHANCEMENT] moved error handling to own controller

__Tasks:__

- [x] test coverage
- [ ] gather feedback for my changes
- [x] submit changes to the documentation


__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | #24 
| BC Breaks     | none
| Doc           | https://github.com/sulu-cmf/docs/commit/7f073fa3af8d1c3a0fb191f626efc9ae7196f6a0