Most playlists sort by artist -> album -> year -> discno -> trackno, but
the Previous playlist sorts by rowid with the most recently added
tracks first, and the Up Next playlist sorts by rowid with the most
recently added tracks last.
Implements: Issue #13 (Give most playlists a default sort order)
Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>
This gives us access to the new functions and built-in caching. I also
change the PlaylistState object to cache its values rather than querying
the database for everything.
Implements: Issue #11 (Cache database items fields)
Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>
