Claymores & Mine Tweaks (shiptest-ss13#2988)

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## About The Pull Request

TODO:

- [x] Actually implement claymores (should we let players have
them?)(Cargo?)

- [x] Remove weird sprite shim I made when world icons are merged, add
world icons to mines

- [x] Sprites (this time we actually need them since the placeholder
ones are tgmc & I didn't ask for permission)

Adds Mines that explode when an object passes in front of them & fire an
ammo casing in that direction.
Adds claymores as an implemented example of this- short range, shreds
people at point blank.
Adds World Icons to normal Mines

I had to do some tweaking behind the scenes to implement mobless casing
firing- but I'm pleased to say that fire_casing() can now deal
emotionally with being handed a null user.

Also minorly tweaks explosion devastation, so heavy explosions can only
strip tiles that have already been damaged
You can still immediately strip tiles with devastating explosions
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## Why It's Good For The Game
FRONT TOWARDS ENEMY
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## Changelog

:cl:
add: Directional Mines, implemented as Claymores.
add: Mines now have World Icons
balance: explosions now only strip to space when a tile is already
damaged
fix: Prox mines explode from slightly further away & no longer activate
through walls.
fix: Multiple mines can no longer be stacked on a tile
code: fire_casing() can now be called by non-mobs, allowing objects to
shoot casings.
/:cl:

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code/datums/components/pellet_cloud.dm

@@ -90,7 +90,10 @@
 
 
 /datum/component/pellet_cloud/proc/create_casing_pellets(obj/item/ammo_casing/shell, atom/target, mob/living/user, fired_from, randomspread, spread, zone_override, params, distro)
-	shooter = user
+	if(user)
+		shooter = user
+	else
+		shooter = fired_from
 	var/targloc = get_turf(target)
 	if(!zone_override)
 		zone_override = shooter.zone_selected
@@ -106,8 +109,12 @@
 		RegisterSignal(shell.BB, COMSIG_PROJECTILE_SELF_ON_HIT, PROC_REF(pellet_hit))
 		RegisterSignal(shell.BB, list(COMSIG_PROJECTILE_RANGE_OUT, COMSIG_PARENT_QDELETING), PROC_REF(pellet_range))
 		pellets += shell.BB
-		if(!shell.throw_proj(target, targloc, shooter, params, spread))
-			return
+		if(user)
+			if(!shell.throw_proj(target, targloc, shooter, params, spread))
+				return
+		else
+			if(!shell.throw_proj(target, targloc, null, params, spread, shooter))
+				return
 		if(i != num_pellets)
 			shell.newshot()