partially moved over update()

Demo:
-reduced update()
+removed loop for removing completed aircraft
+removed airport update()

GameWindow:
-reordered blocks
+update aircraft, check collisions, remove expired aircraft, handle
completed aircraft, update airports, check aircraft waiting in airport,
update controls
-added check for removing completed aircraft
+merged with block that handled this event
-added airport update() call in update()
-removed redundant parameter from checkCollisions()
-modified drawMap()
+simplified mouse pointer logic

Airport:
-modified update() to be compatible with GameWindow
+now asks for the parameter it actually wants