Divide LyricsGooglePluginTest into two classes.
Divide LyricsGooglePluginTest into two classes.

Move existing tests into LyricsGooglePluginMachineryTest.
Create LyricsPluginSourcesTest class to check fetching of each source.
Some code was supposed to do that until now but was never executed as we
exited early at the "if not check_lyrics_fetched():" check.

beetbox/beets,SusannaMaria/beets,jackwilsdon/beets,Kraymer/beets,ibmibmibm/beets,Kraymer/beets,ibmibmibm/beets,beetbox/beets,beetbox/beets,pkess/beets,sampsyo/beets,beetbox/beets,sampsyo/beets,SusannaMaria/beets,ibmibmibm/beets,ibmibmibm/beets,pkess/beets,shamangeorge/beets,Kraymer/beets,jackwilsdon/beets,sampsyo/beets,pkess/beets,pkess/beets,shamangeorge/beets,jackwilsdon/beets,shamangeorge/beets,sampsyo/beets,Kraymer/beets,jackwilsdon/beets,shamangeorge/beets,SusannaMaria/beets,SusannaMaria/beets