[FEATURE] Added navigation context in structure

Added navigation context in structure:

__Tasks:__

- [x] test coverage
- [ ] gather feedback for my changes
- [ ] submit changes to the documentation
- [ ] UI (ContentBundle)
- [ ] Tests ContentMapper Interface (SuluTestBundle)


__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | no => SuluTestBundle
| Fixed tickets | https://github.com/sulu-cmf/sulu-standard/issues/121
| BC Breaks     | none
| Doc           | TODO