Revert "More than one aircraft on the screen"

This reverts commit aae9e5a25b99a8f4f4d384ab73bdd96ce0e45431.
Multiple Aircraft refactored

Refactored to work within the architecture laid out.
Notes for revert:
-Airspace.receiveFlight MUST allow external forces to specify the
recieved point, or we can't maintain a consistent flightplan.
+it isn't a function that performs setFlights; it is a controlled
handler for single flights entering the airspace
+from airspace down, this should follow the model (not game logic)
-not much point enumerating airspaces, transfers since to put together a
world around the main airport includes game logic
+(cannot be done unless airports are made singletons, and needs reset
functionality adding)
-cannot effectively enumerate aircraft because there are potentially an
infinite amount.
Notes for commit:
-DummyAirspace added to replace null, to prevent NullPointerExceptions
when functions written later
-Game.generateWorld extended to produce and link named airspaces
+bearings not set intelligently
-game logic in Game.Play() extended
+plane adding moved to (final) place as part of game logic
+temporary logic to add a list of random planes