Continuing support for 'file' data type with new in-request conversion

- Changed delegate signature to take ```id``` instead of ```NSData*``` (type will depend on conversion)
- Don't bother converting anything for 'file' type, just pass along file url (sort of redundant)
- This was done after updating WebServiceManager in Rue and noticing the image loading broke

Not ideal, I know, but at least this way it still supports the way we were using it when we integrated into Rue.