[WCM] MediaBundle documentation

This PR provides the MediaBundle documentation. It is not ready yet, the TODO's are marked in the text.

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | yes
| Applies to    | MediaBundle, DoctrinePHPCRBundle, CreateBundle
| Fixed tickets | All MediaBundle tickets for 1.0

**TODO to merge:**
- [x] update create config
- [x] add teminology section
- [x] add upload security
- [x] add text or remove TODO marks
- [x] bundle standards