feature/media-ui

__Tasks:__

- [ ] finish the code
- [x] gather feedback for my changes


__Informations:__

merge this branch first:
https://github.com/sulu-cmf/SuluMediaBundle/pull/3

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| Tests pass?   | yes
| Fixed tickets | none
| Doc           |  none