[WIP] Feature/global content reset

https://github.com/sulu-cmf/SuluContentBundle/issues/85

- [ ] test coverage
- [ ] finish the code
- [ ] gather feedback for my changes
- [ ] submit changes to the documentation


| Q             | A
| ------------- | ---
| Bug fix?      | [yes|no]
| New feature?  | [yes|no]
| Tests pass?   | [yes|no|none]
| Fixed tickets | [yes|no|none]
| Doc           | [url to doc|none]