GENERAL ISSUES:
- we need a way for a notification whenever the contents of
  a directory in the database are changed. Maybe we just use
  the standard notification schema and add a generic 
  handling routine (instead of artistaddedtosongdb & Co).
  Maybe we just use the songchanged events, which will
  be parsed by the active view!
  Similarly, playlist should appear in playlist dir when saved

BUGS:
- autoplay=true or autoplay=false for secondary player?
- what happens to mpg123 when pytone crashes
- song is not registered as currently being played, when its playback
  is resumed after a restart of PyTone (in particular, player window
  titlebar is wrong)
- check deleting of songs (reported by Sam Rowe), especially double indexed songs.
  WFM

BEFORE RELEASE:

USER WISHLIST:

- more than 2 database
- allow user to turn the secondary player on and off (or alternatively to stop it)
  (requested by Stuart Pook)
- streaming sources
- create subdirs for artist only if there are more than a certain number of songs 
- Fish: Song der auf zweitem Player kommt, anzeigen

- General:
  o calling of external programs from within python
  o timer interface
  o user authentication and permissions
  o allow up- and download of songs
  o make automatic backups of database
  o database reconstruction
  o consolidate len(self.basedir)
  o replace all helper.debug with log.debug and rewrite log code accordingly.

- Performance improvements:
  o move number of decades, genres, playlists (do it like for songs)
  o make length calculation of filtereddecade and filteredgenre smarter

- UI Improvements:
  o improve behaviour on scroll bar mouse clicks
  o scrollbars are sometimes too short
  o list of seldomly played songs
  o make showing of last added list configurable (similarly for rest)
  o visual indicator that PyTone is busy
