Added sounds for helicopters:
- SOUNDS/en;landin.wav;landing
- SOUNDS/en;idleu1.wav;idle up 1
- SOUNDS/en;idleu2.wav;idle up 2
- SOUNDS/en;normod.wav;normal mode
- SOUNDS/en;bank-0.wav;bank 0
- SOUNDS/en;bank-1.wav;bank 1
- SOUNDS/en;bank-2.wav;bank 2
- SOUNDS/en;bank-3.wav;bank 3
- SOUNDS/en;headlo.wav;heading lock
- SOUNDS/en;ratmod.wav;rate mode
- SOUNDS/en;3d-mod.wav;3D Mode
- SOUNDS/en;stabmo.wav;Stabilize Mode
- SOUNDS/en;on.wav;on
- SOUNDS/en;off.wav;off