release:
-   highlight current song in playlist

other TODO:
- don't quit by closing mainwindow?
- more advanced search in library?
- playlist mgmt (moving items, drag&drop, saving/loading playlists)
- multiple playlists
- queueing (MPD feature?)
- spectrum analyzer
- tagger
- split library by letters (like Amarok)
- icons could use some improving
- waste less memory (library and playlist are main suspects)
- Lyrics - should use only Qt's xml functions and allow user to select lyrics