Make the max-flyBy angle configuable, since for exmaple AIrbus uses 90
degrees. Expose this via a new gps/config property, and extend the tests
to verify that angles greater than the fly-by angle behav as fly-over
waypoints.
Extend the RoutePath code to share this configuration, so that route
visualisations match the configured angle.
SF-ID: https://sourceforge.net/p/flightgear/codetickets/2694/
08a70297ff