-closes #3274

Fact* espVersion = getFact(FactSystem::ParameterProvider, MAV_COMP_ID_UDP_BRIDGE, "SW_VER"); crashes unit test if the parameter does not exist (which is exactly what the call is trying to establish).

Refactored PX4 radio config to work with both PX4 and APM

- MultiVehicleManager is a Qml friendly replacement for UASManager
- Vehicle is a replacement for both UAS and AutoPilotPlugin

- FirmwarePlugin is the new place for code which is specific to
firmware flight stack
- FirmwarePlugin currently supports flight mode apis
- Modify code to use new FirmwarePlugin support

QGCUASParamManager and friends are replaced by FactSystem