tracker-extract-vorbis.c: Extract MusicBrainz IDs for ogg files
Tracker needs to store MusicBrainz IDs to allow retrieval of tags and cover-art in GNOME Music. If a file already has MusicBrainz IDs, then extractor should detect and index them. Extraction of MusicBrainz IDs is done based on tags used by ogg files.
Closes #70 (closed)