v0.31.0: Cassette followed playlists — a friend's playlist in your sidebar

- A followed playlist (the UFO in friend mode) appears in my sidebar with
  a purple UFO: mixed in with my playlists alphabetically, or inside a
  folder named after the friend (per-friend, in Sync Settings). It's never
  a Playlist of mine, so it stays out of the library and its merges.
- It plays from the cache. Player's queue accepts friend-track keys,
  resolved through Cassette: they scrobble to Last.fm but don't count in
  my play journal. Songs still on their way are grey and skipped.
- The cassette column there is hidden by default (right-click the
  header); pressing one takes the song into my library — straight from
  the cache if it's there, otherwise by asking for it.
- Sync Settings per friend: keep followed songs separate (default) or add
  them to my library. Unfollowing (right-click) frees their cache.
- The bottom bar says when the friend's folder last synced.

lintunes/__init__.py

@@ -1,3 +1,3 @@
 """LinTunes — iTunes-style music library manager and player for Linux."""
 
-__version__ = "0.30.0"
+__version__ = "0.31.0"