Option to scrobble only first artist

This adds an option to only scrobble the first artist in case of multiple artists. E.g. Spotify tags tracks with "Artist A, Artist B" if multiple artists collaborate on the same track. This is send to Last.fm as artist="Artist A, Artist B" (a concatenated string). Last.fm does not recognise that as two separate artists, but sees it as one unknown artist. With this option, it will only send the first artist, "Artist A" in this case, keeping the scrobbles to Last.fm clean and correct.
The default option is the current option to concatenate artists. A user must manually change this settings.
Sure:
http://forums.slimdevices.com/showthread.php?79706-Announce-Spotify-Premium-Plugin-%28Beta%29&p=718130&viewfull=1#post718130
http://forums.slimdevices.com/showthread.php?96455-Possible-to-fix-double-artist-tag-from-Spotify
http://forums.slimdevices.com/showthread.php?97470-Fix-for-multiple-artists-scrobbled-from-Spotify
But no response. That's why I decided to fix this myself. I can understand that you probably do not want to merge this patch as such.
I'll see if I can either fix this in Triode's code, and apply the fix there, or see if there is a more general solution that does not depend on any plugin variables.