Let's give cmus a try

cmus has both song change events and a good remote cli.  Let's see if I can replace rhythmbox.

* cmus_event script does libnotify popup on song change
* Added a section to my dzen response to move that notification to .music.out for xmobar.  This was a little uglier than expected because I couldn't convince notify-send not to include its own name in notifications.  pynotify can, but it's slower and another dependency.  Ended up parsing out notify-send, but only when there was another app name.  Ugh.
* Added commands my my generic music client so key bindings work on all my clients.