Instead us a Toolbox concept which hangs off of QGCApplication

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

This function is called automatically when a QSettings object is destroyed,
so is rarely needed to be called explicitly.

There are still some cases where
a QSettings object is passed-by-reference, so there I left the sync() calls as
it's unclear how permanent those objects are and if they'd call sync() before
application shutdown

also adds AMSL output in ft

This patch fixes a bug that display 0 for distances to waypoint more
than 10km.

Besides that, it also homogenize the naming of the label to
"distToWaypoint" instead of "distToWP". Old configuration files (in
home directory), should be hacked or removed in order to see this
change.

Signed-off-by: Paul Chavent <paul.chavent@onera.fr>

Altitude splitted to altitudeAMSL and altitudeRelative, speed splitted to airSpeed and groundSpeed. PrimaryFlightDisplay uses airSpeed for FW and groundSpeed for MC.

Replace 9 seperate valueChanged() signals with just 1, and remove the resultant tons of code duplication

Change so UASQuickView font sizes are now identical, and change properly based on window size and column count

Some comment cleanup, and fix so when closing the main window, it also closes the item select window

Finished merging QGCVehicleConfig.ui, which I hadn't done properly last night. Things are now in a usable state again.

Removing UASes now returns the UI to an almost pristine state. This was done by altering the activeUASSet signal so that it can emit a NULL UAS. Crashes may still exist in autopilot-specific code.

Changes go UASQuickView handles resizing better, and doesn't "clip" text when the window is too small.

Fix for crash when removing item from QuickView, and addition of more generic signal/slot combonation for property updates

Added satelliteCount to the QuickView, and made quickview a default display on the mission planner view.