[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
Why not

````php
$structure = $structure->toArray();
````

?