[WIP][FEATURE] Introduct content navigation groups

__Tasks:__

- [ ] test coverage
- [ ] gather feedback for my changes
- [ ] submit changes to the documentation

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | none
| BC Breaks     | Instead of `NavigationItem` the new `ContentNavigationItem` should be used for the ContentNavigations
| Doc           | will be changed in https://github.com/sulu-cmf/docs/blob/master/developer-documentation/000-foundation/content-navigation-integration.md