Clean up parameter meta data version methods to match spec

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

QGCUASParamManager and friends are replaced by FactSystem

Also updated parser for new xml format

This way you don’t need to know parameter set ahead of time.

Plus a large number of other changes to allow for orderly shutdown of
objects without crashes or asserts. This is need for unit tests to
create/delete global state around every test.

Allows parameter access from QML among other things