Establish a global system state machine

[DNedic]

Generally, launching and flying an UAV will have several steps, from turning on its power, to programming flight parameters and performing pre-flight calibrations, to arming and takeoff etc. Some of these steps are required for safety and some are there simply to ensure correctness before taking off. Additionally, most embedded systems have a simple top-level state machine with an operating and failsafe mode at the very least.

We should implement such a state machine, log and inform telemetry receivers on state changes. For a starting point, we could use Mavlink's MAV_STATE.