preview component

added preview component for content

- [x] finish the code
- [ ] gather feedback for my changes
- [ ] submit changes to the documentation


| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| Tests pass?   | none
| Fixed tickets | none
| Doc           | none

merge first:
https://github.com/massiveart/husky/pull/253
https://github.com/sulu-cmf/SuluAdminBundle/pull/79