column navigation

column navigation for nodes (pages-/content-elements)

- [x] finish the code
- [x] gather feedback for my changes
- [x] submit changes to the documentation


| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| Tests pass?   | none
| Fixed tickets | none
| Doc           | API https://github.com/sulu-cmf/docs/blob/master/detail-specification/300-webspaces/DET-306-node-api.md#example-uri