Ordering of page changed when node is renamed

See #518 

__Tasks:__

- [x] test coverage
- [ ] gather feedback for my changes

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | [YES]
| Fixed tickets | [#518
| BC Breaks     | NO
Added some node traversal methods to the SuluNodeHelper. I think this makes sense.