[FEATURE] Navigation performance (loaded with content query)

__Tasks:__

- [x] test coverage
- [ ] gather feedback for my changes

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | no => https://github.com/sulu-cmf/sulu/pull/263
| Fixed tickets | https://github.com/sulu-cmf/sulu-standard/issues/201
| BC Breaks     | yes => TODO
| Doc           | TODO
The reason I refactored all of those classes to use `->toArray` was actually triggered by this use case. The idea was that we wouldn't have to update this everytime we add something new to those classes.

The current template does not work like that however, and it displays the fields manually - so we can handle medias as a special case /there/ no?