Thermite Effectiveness Scaling with Volume

-The more thermite is applied to a wall, the faster it will burn
-Scales between approx 10-25 seconds
-Rwalls have a higher minimum threshold and burn time
-Applying thermite to a wall now leaves a visible stain on the wall

Conflicts:
	code/game/turfs/simulated/walls.dm
	icons/effects/effects.dmi

code/modules/reagents/Chemistry-Reagents.dm

@@ -1122,11 +1122,14 @@ datum
 
 			reaction_turf(var/turf/T, var/volume)
 				src = null
-				if(volume >= 5)
-					if(istype(T, /turf/simulated/wall))
-						T:thermite = 1
-						T.overlays.Cut()
-						T.overlays = image('icons/effects/effects.dmi',icon_state = "thermite")
+				if(volume >= 1 && istype(T, /turf/simulated/wall))
+					var/turf/simulated/wall/Wall = T
+					if(istype(Wall, /turf/simulated/wall/r_wall))
+						Wall.thermite = Wall.thermite+(volume*2.5)
+					else
+						Wall.thermite = Wall.thermite+(volume*10)
+					Wall.overlays = list()
+					Wall.overlays += image('icons/effects/effects.dmi',"thermite")
 				return
 
 			on_mob_life(var/mob/living/M as mob)