Updated playlists to work with iTunes 5.

Added PlaylistNode class to handle the playlists menu, since it is nested now.
Support for nested folders in iTunes
Completely rewrote playlists methods. Podcasts menu item shows up in the proper place now too.
iTunes 5 orders sources differently than iTunes 4, as far as I can tell. Instead of doing weird indexing like iTunes 4 (1, 2, 3 (skipped if there's no CD), 4, 5), it counts linearly all the time. I need someone with iTunes 4 to be sure this still works in iTunes 4 though.