Better handle the dirty state of Airmap's flightplan

Object ownership handled by SettingsGroup base class

Get rid of QGCView, QGCViewPanel and FactPanel. All messages and dialogs are now handled in the root window.

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

Add control to set flight duration (which ultimately sets the end_time of flight)

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

More clang warnings cleanup

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.

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).

Make the choice of using a personal key persistent. This will allow to toggle between personal and hardcoded key. Otherwise you would need to clear your personal key each time you want to use the hardcoded one.