Add initial SITL simulator support

[DNedic]

Most autopilot projects support some sort of software in the loop simulation, in order to not have to actually use a vehicle for basic testing. This is extremely helpful, since some things can't be covered by unit nor integration tests, and having an aircraft crash every time there is a bug in the flight
code is prohibitively expensive and sometimes even dangerous. Ideally, we should strive to have this before putting to use stabilized or autonomous flight modes.