You can't take the length of a playlist folder:
```
Exception in thread Thread-2:
Traceback (most recent call last):
  File "/usr/lib/python2.7/threading.py", line 552, in __bootstrap_inner
    self.run()
  File "jukebox.py", line 37, in run
    self.cmdloop()
  File "/usr/lib/python2.7/cmd.py", line 142, in cmdloop
    stop = self.onecmd(line)
  File "/usr/lib/python2.7/cmd.py", line 221, in onecmd
    return func(arg)
  File "jukebox.py", line 82, in do_list
    print('{:>3d} {:>20} ({} tracks)'.format(i, name, len(p)))
TypeError: object of type 'spotify.PlaylistFolder' has no len()
```