Convert the route-manager to use a flight-plan internally, and expose
flightplan, leg and procedure data to Nasal. Move the Level-D parser
into its own file.
Supports various new editing features, including dragging to re-order, and
+/- keys to adjust the target altitude for a waypoint. Also displays some
additional information, and will display *even* more once I land airways/
SID/STAR support.