Mouse support (and tweaks)

New feature:

You can now control the ailerons and elevators with the mouse. The mouse buttons control the flaps (and also dismiss dialog messages).

Mouse is enabled in the pause menu.

Changes

Fixed bug where waypoints could occasionally wander off screen and disappear.

Updated Pitts Special model to make the canopy more visible.

Made landing vertical speeds more forgiving. Previously the limits were:

• >250 ft/min = "hard" (fails the "soft landing" mission objective)
• >350 ft/min = "crash" (causes damage)

The limits have been changed to:

• 350 ft/min = "hard"
• 500 ft/min = "crash"