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.

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

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

Also rename QmlPageInfo to QmlComponentInfo to cover more use cases

Used to display items associated with Flight Plan on Map