Lots of (pretty hacky) changes specific to our SteamOS setup:
* Replaces most JSON RPC commands with EventClient commands
  - This means that the commands come through to XBMC as "remote" keypresses and are context-aware
* Adds the AUDIO_SYSTEM device type, so that the TV mutes its internal speakers and sends volume controls via CEC
* Handles volume key presses (VOLUME_UP, VOLUME_DOWN, MUTE) with PulseAudio volume adjustments
* Adds a handler which calls a 'return to desktop' script
  - (We use this so that we can go from the Steam interface to the XBMC interface)