Added ability to interface with Cmus

Added simple system commands to invoke cmus-remote instead of pandora if
I would like to play music locally. This is a quick and dirty way of
doing it.
Replaced polling with triggers

Instead of polling every 500 milliseconds for changes in the pins in a
loop, we use event triggers in the form of waitAny. This allows us to
have better responsiveness to button presses.
Merge branch 'master' of https://github.com/changlinli/remote-arduino-music

Conflicts:
	RemoteMusic.hs
Revert to 627ab8a31a34f98abe7d8cc46e0ae27d35dc164c

Reverting the master branch back to last known good state.