Change language in admin

Added the `ProfileController`, which is not secured, and changes the currently logged in user.
Merge together with https://github.com/sulu-cmf/sulu-standard/pull/388

__Tasks:__

- [ ] test coverage
- [ ] gather feedback for my changes

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | fixes #615 
| BC Breaks     | none
| Doc           | none
@danrot shouldnt this be a rest-controller like /user/me ?