sulu-cmf/sulu-standard#125 Copy locale ui

__Tasks:__

- [x] test coverage
- [ ] gather feedback for my changes

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | fixes sulu-cmf/sulu-standard#125
| BC Breaks     | none
| Doc           | none
AFAIK the FOSRestBundle sets the status code automatically to 204 if there is no content.