Spectrum2/backend.py:handleDataRead is called when transwhat receives
data from Spectrum. The parameter `data' contains multiple (or pieces
of) WrapperMessages. Instead of passing all the data to
wrapper.ParseFromString. We should only pass a single WrapperMessage.
When a whatsapp buddy sends an image, video or sound to the spectrum
user, the spectrum user will receive a URL that links to the media.
FileTranfer in spectrum is not working, apparently. Thus media cannot be
sent yet.