Altimeter buttons fixed

Altimeter:
-added mouseDownState to track mouse action
+to take constants NONE, TOP, BOTTOM (arrows clicked)
-added helper function getMouseState()
-modified mouseReleased()
+determines mouse state and colours buttons accordingly
+white for mouse over button that you first clicked
+transparent green for mouse over button you did not click
+else opaque green
-modified draw() to take and pass on mouse position
-modified drawAltitudeArrows() to use mouse position to determine hover
colour
-removed parameterless MouseOver() functions
+cannot be calculated without the drawing context