Add ALBUMARTIST tag support for Cue files

Interpret and export the top-level PERFORMER in the Cue file as the ALBUMARTIST tag.  If the per-track PERFORMER (e.g. track artist) is different, flag this album as a compilation.

This also helps LMS recognize multi-disc sets of compilations (when using cue sheets).
Merge remote-tracking branch 'mrthreeplates/add-albumartist-cue' into public/7.9
Changelog update.