Spectacular improvement in traffic manager initialization and preparatory

Spectacular improvement in traffic manager initialization and preparatory
work for ground based distance separation of AIAircraft.

Traffic manager initialization related changes:
- Schedules initialize "on the fly", instead of during initialization
- Invalid routes are no longer deleted, but marked as BOGUS and ignored
- Changed loading order from a distance based prioritization to a point-
  score based prioritization, resulting in a much faster establisment of
  AIAircraft near the user's plane.

Preparatory work for ground-based separation of Aircraft.
- The groundnetwork findShrortestRoute function not only returns a list
  of waypoints, but also a list of taxi "segments" (a.k.a. taxiways).
- The taxiway list is stored in the Flightplan, and updated everytime
  a new taxi leg is created.