Move cache for preview to Doctrine Cache

__Tasks:__

- [x] test coverage
- [ ] gather feedback for my changes
- [x] StructureSerializer
- [x] CacheProvider
- [x] remove temp node


__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | none
| BC Breaks     | https://github.com/sulu-cmf/sulu/commit/5eb485813c29fab3b6ed1d51aca9cee09f7c71b9
| Doc           | none
We are running in trouble last time with the serializer so i think it is better todo it for our own and the class you see is really small and i think it is a better solution than doing it with the jms serializer! /cc @chirimoya ??