Plus new unit tests

It is also no longer a user visible field

# Conflicts:
#	src/MissionManager/MissionManagerTest.cc

Also additional major Mission usability changes

- override by vehicle type
- override by firmware type

- Fix: Version error message not being displayed
- Correct handling of APM and PX4 files with respect to home position
in first slot
- Emit newItemsFromVehicle signal so editor can fit map viewport on
load from vehicle

Previous order was signalling new mission items available prior to in
progress going false. This was causing MissionController to pull an
empty mission list.

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