Added user-agent string ('r3tagger') in query.musicbrainz. Took me forever,
but in my defense, there were no docs about how to do it properly and I had to
go through the source. Added logging for query.Retry to keep a list of
WebServiceError occurances. Created script for toggling the musicbrainz api
mock. Tested tests/test_Musicbrainz without the mock enabled (been forever)
and everything still passes.