[FEATURE] preview in the sidebar

__Tasks:__

- [x] delete the preview component
- [x] make the preview use the new sidebar
- [x] implement switch preview resolution
- [ ] gather feedback for my changes

__Informations:__

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| Tests pass?   | no => https://github.com/sulu-cmf/sulu/pull/123
| Fixed tickets | none
| Doc           | TODO