Aircraft rendering tidying

-image set up as it should display for bearing 0
+(up is forwards; rotate around centre of image)
-Aircraft rendering:
+rotated image generated as needed in draw()
+setBearing() written to invalidate image
+rendering uses rotatedImage properties
-TransferWaypoint modified to be more useful
+getBearingTo() and getBearingFrom() functions
+(no need to manage +-pi with corrections to stay in 0-2pi range)
-test code added to rotate plane to see effects
-Airspace reverted to use Flight types