Add hooke.playlist.NoteIndexList and refactor exception handling in commandline.

Add hooke.playlist.NoteIndexList and refactor exception handling in commandline.

Highlights:
  * hooke.playlist classes now subclass the new hooke.playlist.NoteIndexList
  * hooke.plugin.cut.CurveArgument replaces previous _run hacking with
    a callback to initialize the default curve.x
  * hooke.ui.commandline.command_parser -> CommandLineParser.  The new
    class is cleaner, and raises exceptions rather than exiting.  We
    don't want Hooke dying until the user has time to clean up.