#2551 REST Cleanup: Blog metadata

- Implemented post format sync in REST
- Added batched sync of options and post formats in REST
- No more media syncing
- Removed temporary BlogServiceRemoteProxy

Note I branched from #2570 so make sure to review/merge that one first

Refs #2551 
Code was moved from somewhere else, so I'm not 100% sure why it's that way. I vaguely recall different response formats, but while it could be written with SafeExpectations, I see a few reasons why not:
- If responseObject[@"supported"] is not an array, it's already in the wanted format. We don't want nil, we want "self"
- `arrayForKey:` is only defined for dictionaries, so we'd still have to check that `responseObject` is a dictionary