[musicdb] infoscanner updates
[musicdb] scan optimization - skip the scan if we don't find any music in the dir
[musicdb] fix artist fanart in infoscanner
[musicdb] add artist contributions (artists can have different names on individual songs/albums)
this allows for artists that have different names on some albums and songs
e.g. think about Prince vs TAFKAP - some albums have credits as prince, some as symbol
[musicdb] drop use of GROUP_CONCAT in albumview and instead use album.strArtists
[musicdb] construct the artist string from the artistCredits
[musicdb] fix: no longer force people to the musicbrainz scraper for MBID tagged music