partial game logic separation, resizing extension

Demo:
-removed redundant highlighted_altitude variable
-removed location_waypoint variable
-removed airport.loadImage() call
!should be handled internally by Airport after the merge

GameWindow:
-added private scale variable
+calculated in setAreas()
-added gameArea Rectangle to prevent recalculations
+initialised in constructor
-reduced visibility of airport to private
+initialised in constructor
-added locationWaypoints
+initialised in constructor
-setAreas() extended
+scales gameArea height in proportion to width
+fills remaining vertical space with controls