[WIP] [FEATURE] Added categories and tags to excerpt tab

Additionally added except.xml to generate excerpt form with the form generator

__Tasks:__

- [x] test coverage
- [ ] gather feedback for my changes

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | no => sulu/sulu
| Fixed tickets | https://github.com/sulu-cmf/SuluContentBundle/issues/178
| BC Breaks     | none
| Doc           | none