Smart Content

Introduces smart content, dependent on https://github.com/sulu-cmf/SuluSecurityBundle/pull/32 and https://github.com/sulu-cmf/sulu/pull/43

- [x] test coverage
- [x] finish the code
- [ ] gather feedback for my changes
- [ ] submit changes to the documentation


| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| Tests pass?   | yes
| Fixed tickets | none
| Doc           | https://github.com/sulu-cmf/docs/blob/master/detail-specification/100-basic/DET-105-SmartContent.md