Bugfixes and some finetuning:

Bugfixes and some finetuning:
* Pregenerating taxiroutes could interfere with runway assignments by ATC, when conditions changed, resulting in a taxi to one runway and a takeoff from another
* A simpler solution for the "Error in Traffic record bug". This still needs some more testing, but I haven't seen any error message anymore, since changing to the current code.
* Initialize AI traffic at speed zero, this should prevent some weirdness observed under boundary conditions.
* Don't activate groundnetwork proximity detection for pushback traffic until the "ready for startup message is transmitted. this should allow sufficient time for them to reserve a route, but a little more testing still needs to be done.