Changes obj/effect/blob,spider,swarmer,energy_net,spacevines to be ob/structures instead, since you can hit and destroy them.

Adds a large ash and large molten item decal (for future use)
simplifies decal/cleanable/replace_decal() code a bit.
Changes construction() proc to on_construction() for consistency, same for deconstruction().
Made a deconstruct() proc for machinery and computer (also for future use).

code/game/objects/items/weapons/chrono_eraser.dm

@@ -255,7 +255,7 @@
 /obj/effect/chrono_field/ex_act()
 	return
 
-/obj/effect/chrono_field/blob_act(obj/effect/blob/B)
+/obj/effect/chrono_field/blob_act(obj/structure/blob/B)
 	return
 
 

code/game/objects/items/weapons/grenades/flashbang.dm

@@ -12,7 +12,7 @@
 	for(var/mob/living/M in get_hearers_in_view(7, flashbang_turf))
 		bang(get_turf(M), M)
 
-	for(var/obj/effect/blob/B in get_hear(8,flashbang_turf))     		//Blob damage here
+	for(var/obj/structure/blob/B in get_hear(8,flashbang_turf))     		//Blob damage here
 		var/distance = get_dist(B, get_turf(src))
 		var/damage = round(100/(distance*distance)+1)
 		B.take_damage(damage, BURN)

code/game/objects/items/weapons/grenades/smokebomb.dm

@@ -24,7 +24,7 @@
 	smoke.start()
 
 
-	for(var/obj/effect/blob/B in view(8,src))
+	for(var/obj/structure/blob/B in view(8,src))
 		var/damage = round(30/(get_dist(B,src)+1))
 		B.health -= damage
 		B.update_icon()

code/game/objects/items/weapons/holosign_creator.dm

@@ -136,7 +136,7 @@
 	..()
 	take_damage(I.force * 0.5, I.damtype)
 
-/obj/effect/overlay/holograph/blob_act(obj/effect/blob/B)
+/obj/effect/overlay/holograph/blob_act(obj/structure/blob/B)
 	qdel(src)
 
 /obj/effect/overlay/holograph/attack_animal(mob/living/simple_animal/M)

code/game/objects/items/weapons/tanks/tanks.dm

@@ -91,7 +91,7 @@
 
 	user << "<span class='notice'>It feels [descriptive].</span>"
 
-/obj/item/weapon/tank/blob_act(obj/effect/blob/B)
+/obj/item/weapon/tank/blob_act(obj/structure/blob/B)
 	if(B && B.loc == loc)
 		var/turf/location = get_turf(src)
 		if(!location)