Switch to using firmware manifest for ArduPilot flashing

Update ArduPilot version to latest releases only

Add support for geofence return point. Also fixed a bunch of bugs in geofence and rally point support.

Offline Maps: Allow custom build settings overrides

ArduPilot for configurable mavlink stream rates

Support for new AltitudeFactTextField

Expose guided altitude settings. Rearrange Fly and Plan view settings.

Add new Help page under Settings

* QGCCheckListItem -> PreFlightCheckButton
* CheckList -> PreFlightCheckList

The LinkIndicator shows the connected links and lets the user select the priority link,

Automated preflight checklist: Initial commit. Note that this requires an autopilot firmware that writes the respective health flags in the SYS_STATUS mavlink message

Create a "Dead Mouse Area" control to eat mouse events underneath desired area. This is to prevent mouse events from leaking through controls underneath the area.
Replace original "NoMouseThroughRectangle" as this is more versatile.
Prevent mouse through events from leaking underneath the Fly View tool strip.

Move all airmap related stuff to its own directory

Moved "Grid Lines" out of General Options and into the Video Stream Widget
Made a QGC custom Switch element

Added AirMap settings (SettingsGroup)
Added AirMap settings block to General Settings
Create macros to deal with the tedious repetitions within SettingsGroup
Removed old, hacked in setting for AirMapKey
Remove a few of the tons of build warnings

Converted Structure Scan to use CameraCalc such that it now works with
camera specs.