Support for reading new Vorbis cover art

http://wiki.xiph.org/index.php/VorbisComment#Cover_art

https://bugzilla.gnome.org/show_bug.cgi?id=689420
Support for writing new Vorbis cover art

http://wiki.xiph.org/index.php/VorbisComment#Cover_art

https://bugzilla.gnome.org/show_bug.cgi?id=689420