Rebuilt the tvrage backend.

As the XML backend of TVRage is very unreliable, I had to reconsider using it
to acquire the TVRage ID I need. I found that the quickinfo tool is a lot more
reliable but the format is borderline insane.

As reliability trounces over sane formatting, I'm now using that to find the
matching TVRage ID. I also changed the way how I verify if it really is the
correct show by comparing the airdates of the first episodes of every season.
Drastically change how testing is done.

Added a module that mocks all requests calls during testing if USE_NETWORK is
not set. This was always the plan but as the tvrage API was found too
unreliable to develop against, it had to be implemented sooner rather than
later.

This commit also contains the test data that's needed to succesfully mock all
requests.