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

If Facts are referenced from FactPanelController, we need to reference
count the AutoPilotPlugin such that it doesn’t get destroyed until
after the FactPanelController is destroyed.

Also removes qextserialport

More consistent with Qml usage pattern

- Much simpler UI
- MVC style qml programming model

Fixes Issue #1162

UAS may be around at constructor time

UAS may be around at constructor time

Starting point for real implementation

Summary page is also the launching spot for the setup screens. No more
left hand set of buttons.

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.

- allow unit tests to use QGCApplication
- clear global singletons for each unit test run