Wrap errors sent with RAC's "sendError" with the appropriate status code, update Sample project to build with new status code requirements

This is basically what I had in mind for https://github.com/AshFurrow/Moya/issues/46. I'm not sure if this is a great approach or not - I don't _think_ that client code would ever need to know the actual error code vs the status code sent from the server. If so the http status should probably be added to the userInfo and documented?