[FEATURE] Content search

__Tasks:__

- [ ] gather feedback for my changes
- [x] index definitions (https://github.com/sulu-cmf/sulu/pull/215)

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | #211 
| BC Breaks     | none
| Doc           | TODO @dantleech