Basic Pithos Support for Now Playing Segment

This could easily be expanded to support more formatting options, but I wanted to request this be pulled since it's rather simple and works.

Provides $artist - $song format for Pithos. If Pithos is not playing, it does not print anything.

For information about Pithos:
http://kevinmehall.net/p/pithos/

And the Pithos dbus API:
http://bazaar.launchpad.net/~kevin-mehall/pithos/trunk/view/head:/pithos/dbus_service.py