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)

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.

Change feature default values to something that will be identified as "not set". When a flight is created, features with missing values (not set) are not included. Note that all these are persistent, which may create a problem if something changes (different vehicle with large weight difference for instance). As the subsequent use of these are persistent, a question may not be asked because it's already set (the brief only asks for missing or problem values).

Add message asking user confirmation to end a flight

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

Fix sorting issues with QmlObjectListModel
Show airspaces in Plan View as well

An rather unfruitful attempt at consolidating Advisories and Airspaces (they are both arrays of Airspaces). No such luck as they vary wildly. In the end, I'm now exposing the restrictions (Polygons) directly (and inherently) instead of copying them.
Tweaked polygon overlay colors and borders.

Users can select multiple rules concurrently. In addition, some are mutually exclusive. Add logic to handle this.

Break apart string of classes into their own files as all in one file became unwieldy
Expose Airspace data in a QML ready format
Split global Airspace from AirMap (Only now I figured out the reason for the pure virtual root classes)
Refactored a bunch of things to make it consistent and/or obvious