Add test for MusicBrainzClient.
Parse discid xml from MusicBrainz correctly. Fixes #4025.
Reset the model during init of CddaDevice

This ensures that the track list in the device tab is correctly updated when a
disc is replaced with one that doesn't exist in the MusicBrainz database.
Make mock_network_ a std::unique_ptr and create it in SetUp() instead of SetUpTestCase().
Move qRegisterMetaType back to SetUpTestCase(). Add comment
regarding ownership of the optional argument to MusicBrainzClient().
Merge pull request #4375 from paperbagcorner/fix-musicbrainz

Fix parsing of MusicBrainz data for discid