EZP-20172: Refactored object visiting

Got rid of QaFoo\RMF\Message, visitors will return
an HttpFoundation\Message.
EZP-20172: Added CachedValue REST objects + visitors

- /content/objects/{contentId}
- /content/objects/{contentId}/locations
- /content/objects/{contentId}/versions
- /content/objects/{contentId}/versions/{versionNumber}
- /content/objects/{contentId}/versions/{versionNumber}/relations
- /content/objects/{contentId}/versions/{versionNumber}/relations/{relationId}
- /content/locations/{locationPath}
- /content/locations/{locationPath}/children