Comment 3 for bug 502989

Picking the bug, since I'm responsible for this mess. Things to do:

panel/playlists.py:
- generate playlist content only when expanding, and free the treepath when collapsing
- do something only if the changed tag is one among title/artist/albumartist
- only update currently expanded playlists
- do so via a function that will search for the changed track and only refresh this one

Collection:
- do something only if tag is among (title/artist/albumartist/date/genre/composer/any other relevant tag) - might be more clever to do something if ! among a list of internal tags

Playlist:
- do something only when the tag is among the displayed ones, otherwise we really don't care

This should be enough to make the GUI more responsive than it is at the moment.