Implement MediaService getMediaWithId in REST and XMLRPC.
Don't keep reference to featuredImageCell while loading media.
Force featured image to be always active.

This was done in order to circumvent the issue that the REST API always return this field as FALSE.
Implement uploadMedia on MediaService.
Make featured image cell show upload status immediately after selection.
Merge branch 'develop' into feature/media_services_implementation
Fix formatting and naming style.
Refactor variable name to reflect type.
Refactor code to use operation method on upload.
Fix error message formatter.
Remove unnecessary return.
Refactor getMedia to always hit the network and make findMedia public.
Merge branch 'develop' into feature/media_services_implementation
Remove unnecessary calls to the main queue.
Fix type error.
Remove hardcode value, waiting for fix in the API.
Merge pull request #2642 from wordpress-mobile/feature/media_services_implementation

Feature/media services implementation