Autoupdate & Playlists Folder Sync-Delete Support

This release adds the functionality of managing the "Playlists" folder created
at the selected destination. The prior version would delete songs in the
destination playlist folder that were no longer in that particular playlist,
but would not remove a playlist folder itself if the user deselected it. I did
this to support people manually setting up their own playlist folders. By
request I now treat the "Playlists" folder the app creates as owned by the app,
and it will delete any files and folders that aren't part of the currently
selected set of playlists.

Also, this release integrates the Sparkle project for update notifications and autoupdate
functionality.