block content type

block content type:

- [x] test coverage
- [x] finish the code
- [ ] gather feedback for my changes
- [x] submit changes to the documentation

better description here (sulu.lib should be merged together with this):
 * https://github.com/sulu-cmf/sulu/pull/81

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| Tests pass?   | yes
| Fixed tickets | none
| Doc           | none