more code contracts
Merge branch 'master' of https://github.com/MMessell/Robust-Software-Systems

Conflicts:
	AirTrafficController/AirTrafficController/IPosition.cs
	AirTrafficController/AirTrafficController/Position.cs
	AirTrafficController/AirTrafficController/obj/Debug/AirTrafficController.dll
	AirTrafficController/AirTrafficController/obj/Debug/AirTrafficController.pdb