Refactoring of AbstractAircraftObjectFactory

Hi everyone,

I've replaced the AbstractAircraftObjectFactory class with DefaultFlightPathGenerator and DefaultObjectCreationRate classes since I think it splits things up a lot cleaner than before.

I've also removed the list of waypoints from AirspaceConfig since they are now stored in DefaultFlightPathGenerator - though this may make it a little more complicated if you wanted to draw ALL the waypoints on the screen at once.

Does anyone have any opinions on this - do you think it's better? (and do you understand it)
I did a lot of the other logic stuff - so this is probably the main part of the logic which needs finishing (except the testing)