EZP-20172: Refactored object visiting

- Removed the need for QaFoo\RMF\Message by making Output\Visitor return
  an HttpFoundation\Response directly. The Response object is also used
  internally by the visitor, and can be manipulated directly from
  ValueObjectVisitor implementations.
EZP-20172: Cached REST resources on LocationId

GET /content/objects/{contentId}
GET /content/objects/{contentId}/locations
GET /content/objects/{contentId}/versions
GET /content/objects/{contentId}/versions/{versionNumber}
GET /content/objects/{contentId}/versions/{versionNumber}/relations
GET /content/objects/{contentId}/versions/{versionNumber}/relations/{relationId}
GET /content/locations/{locationPath}
GET /content/locations/{locationPath}/children
GET /content/locations/{locationPath}/urlaliases
GET /user/groups/{groupPath}
GET /user/users/{userId}
GET /user/groups/{groupPath}/subgroups
GET /user/groups/{groupPath}/users
GET /content/binary/images/{imageId}/variations/{variationIdentifier}
Merge pull request #659 from ezsystems/implement/EZP-20172-REST_HTTP_cache

EZP-20172: Location based HTTP cache aware REST API