Add support for Fully's MQTT API

Fully Kiosk Browser can connect to an MQTT server and will publish its full device information every 60 seconds (same info we get from the REST API). It will also publish a variety of events on the MQTT server as they happen (motion detection, ac adapter plugged/unplugged, screensaver start/stop, device movement, etc). We should add MQTT support to this lib alongside the REST API support so we can add triggers based on events.