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.