Add ALBUMARTIST for FLAC

[dsully]

Attached is a patch that adds an ALBUMARTIST tag to FLAC files, if the trackArtist isn't the same as the albumArtist.

[hawk259]

This patch works great when ripping from a CD to a FLAC file, but it doesn't work when converting from FLAC to another format.

I added a patch to Metadata/AudioMetadata.mm that will set the ALBUMARTIST and ARTIST correctly when reading a FLAC file. The code is not pretty, but don't know of a better way while in the tag loop.

Both patches fix my issue where when converting from FLAC files to another format:

{albumArtist}/{albumTitle}/{trackNumber} {trackTitle}

albumArtist was really the trackArtist and putting some songs for a given album in different folders.