Adds more sounds effects (#3474)

Adds new sounds effects to the following;
-nar'sie summoning
-turning on and off a welder
-using a megaphone
-new flashbang and being hit by a flashbang sounds
-cutting wood
-chain of command attack sound
-opening/closing curtains
-rocket launcher sound
-opening/closing a light submachine gun

code/game/objects/structures/curtains.dm

@@ -22,7 +22,7 @@
 		..(P, def_zone)
 
 /obj/structure/curtain/attack_hand(mob/user)
-	playsound(get_turf(loc), "rustle", 15, 1, -5)
+	playsound(get_turf(loc), 'sound/effects/curtain.ogg', 15, 1, -5)
 	toggle()
 	..()