[musicdb] musicdb restructure for musicbrainz artist IDs - remove artist/album ID from CSong and place into artist/album, rewrite the info scanner music database and gui windows, and update the scanners and scrapers to support musicbrainz ID resolution
[musicdb] refactor out FindAlbumInfo and tidy up some common code
[musicdb] implement a per host rate-limiter to avoid hitting the musicbrainz rate-limit and be more friendly to our peers.
[musicdb] support reading/writing compilation flag from the scrapers
[musicdb] support reading/writing song credits from the scrapers
[musicdb] set art properly for musicdb items in the song info view, and set more all artist arts (artist thumbs)
[musicdb] update the music database APIs to be more consistent
[musicdb] update scrapers to support musicbrainz lookups
[musicdb] remove OnManualAlbumInfo - not used in confluence
Merge pull request #2626 from night199uk/musicbrainz

[music] add musicbrainz support to the music library