Update MusicBrainz to support writing the individual artist names to the...

... tags.

This helps clients which scan MB tagged music in an offline mode to correctly index the artists until they can be resolved online. For example when scanning MB tagged music today all of the MusicBrainz IDs have a 1-1 mapping with ID3 tags except the artists:
MusicBrainzAlbumID -> Album Name
MusicBrainzArtistID[s] -> Artist
That means if we're building a database of artists and we hit a track with multiple artists we see 2 MusicBrainz Artist IDs, but only 1 Artist Name. It is therefore impossible to show a good default for the Artist IDs without looking them up online. This helps clients to correctly index the music even without access to MusicBrainz itself.