[musicdb] rewrite the info scanner, music database and gui windows for musicbrainz
[musicdb] update the Scanner & Scrapers to support ID resolution for MusicBrainzIDs
[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. also update the MB scrapers so they cache properly (caching by filename) to remove www. and make http://musicbrainz.org the standard.
[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] cosmetic: update the music database APIs to be more consistent