Fetch classical-related tags from MusicBrainz

[ryanakca]

Please sync the multi-valued tags

• PERFORMER
• CONDUCTOR
• ENSEMBLE
• ARRANGER
• COMPOSER
• etc.
  from MB.

Ideally, this would include what they're credited for. Using this Beethoven work as an example, I'd hope to see something like:

PERFORMER=Norman Scott (bass vocals)
PERFORMER=Robert Shaw Choral (choir vocals)
CONDUCTOR=Robert Shaw (chorus master)
CONDUCTOR=Arturo Toscanini
PERFORMER=Nan Merriman (mezzo-soprano vocals)
ENSEMBLE=NBC Symphony Orchestra
PERFORMER=Eileen Farrell (soprano vocals)
PERFORMER=Jan Peerce (tenor vocals)
COMPOSER=Ludwig van Beethoven

This is inspired from the recommendations on http://age.hobba.nl/audio/mirroredpages/ogg-tagging.html , which builds on the Ogg Vorbis header specification. In particular, the header specification says "Field names are not required to be unique (occur once) within a comment header. As an example, assume a track was recorded by three well know artists; the following is permissible, and encouraged:"

ARTIST=Dizzy Gillespie 
ARTIST=Sonny Rollins 
ARTIST=Sonny Stitt 

This depends on issue 505.

[dosoe]

Maybe #2563 ?