Moving Aircraft

-Airspace
+restored to pre-test logic changes
+visibility of data changed
-Airport receiveFlight()
-Flight setPosition() added
-Aircraft tidied
+unused code removed
+minimal movement logic added
-testAircraft tidied
+no additions to Aircraft currently
-Game loop added
+continuous loop until halt in Game
+Play() and call in MenuDisplay
-Position constructor added (copy existing Position)
-clarify GameTime units