Better handle the dirty state of Airmap's flightplan

Limit all queries to areas smaller than 500km^2. If an area of interest is greater, clip to 500km^2 centered on current ROI's center.
Removed the identifier "Airmap" from error messages coming from Airmap.
Added a clipping function to QGCGeoBoundingCube (clip polygon to given area)

Replacing colors with the ones provided by Airmap.
Adding border color and width.
Adding airspace ID so it can later be linked to the advisory list.

Renamed "Invalid" (airspace) to "custom"

The "Now" button now sets a "now" flag instead of adjusting the start time. Once the flight is created, the actual "now" time is set for flight start time.
The button is also exclusive. Once set, the start time slider is hidden as it becomes irrelevant.

If briefing evaluation returns no authorization, assume none is required. This is reflected in the UI as "Authorization Not Required".

Added some basic color management for airspaces

Handle flight start/end time
Handle start/stop traffic monitor
Only start telemetry if enabled
Added a "Now" button for the flight start time
Collect advisories only when the rules change

Updates in general was only done if a POI changed. This caused changes related to something other than a change in POI to be ignore. The code now "resets" the POI when such changes occur (change of ruleset for example).
Ruleset selection is was not persistent. When reloading the list of rulesets for a given region, any previously selected ruleset would be reset to defaults.
Also fixed several new clang warnings.

It seems the icons now use dash instead of underscore. I'm simply replacing dash by underscore wholesale (to match the existing resource names) until I know better.

Add message asking user confirmation to end a flight

Remove delete flights and add "End" active flight instead
Work on flight geometry (flight list)

Implementing authorization management

Flight management with date range, delete flights.

Cleaning up old vehicle manager and getting it ready to actually provide services for a vehicle (flight management)
Added submit flight plan
Added update flight plan
Disable flight features as these don't seem to be quite working (values must be initialized and validated before submission as backend doesn't validate and the objects don't initialize their members)

Permit refactoring
QGCButton tweaks

Make all argument to AirMap queries based on what the screen shows (bounding rectangle and/or radius), respecting the limits imposed by AirMap.

Collect rulesets from briefing

Moved flight planning away from "Flight Management" to its own class. Planning does not need a connected vehicle.

AirspaceManager is now exposed by QGroundControlQmlGlobal instead of Vehicle (available all the time)