A Pellet Gun! A Recreational rifle for Civilians. (#6628)

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## Civilian Shooting Made Easy!
Many characters on the server may be from societies where firearms are
restricted (after all not everyone has a military backstory) or
otherwise come from peaceful planets. Now living in the dangerous
frontier, they may want to learn to shoot. However, very reasonably the
environment of the station restricts access to firearms. A pellet gun
provides them the opportunity to learn the basics of ballistic firearms
operation without needing security to look over their shoulder. This PR
adds a simple pellet gun and an outdoor range to Atlas. Security can
hand out the pellet guns without worry they may be misused. Civilians
can freely use the pellet guns for recreational purposes or training.
The outdoor range also provides a no-access required public-use facility
for shooting.

The station starts with four pellet guns and four pellet boxes stored in
the security entrance checkpoint in plain-view locker. They simply need
someone with sec access to unlock it and hand it off to people. Single
ones can also be ordered from cargo.

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## Why Not Just Use Donk Soft Guns?
Mechanically not much different but aesthetically/in character they are.
In Character, most people see the brightly colored toy dart gun much
differently from a pellet shooter which resembles a real weapon, NT
probably thinks so too. Consider this, in terms of RP, the middle step
between a character learning to shoot a dart gun versus beginning to use
a real one.

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## Changelog

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🆑
add: a pellet gun and associated icons.
add: two new hangable targets that don't look like people
/🆑

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code/game/objects/structures/crates_lockers/closets/secure/security.dm

@@ -571,3 +571,12 @@ GLOBAL_LIST_BOILERPLATE(all_brig_closets, /obj/structure/closet/secure_closet/br
 	if(prob(75))
 		new /obj/item/storage/backpack/dufflebag/sec(src)
 	return ..()
+
+/obj/structure/closet/secure_closet/pelletguns
+	name = "pellet gun lockers"
+	desc = "Contains some pellet guns and pellets for recreational shooting. Can be issued to civilians without worry."
+	closet_appearance = /singleton/closet_appearance/secure_closet/security
+	req_access = list(ACCESS_SECURITY_BRIG)
+	starts_with = list(
+		/obj/item/gun/ballistic/caseless/pellet = 4,
+		/obj/item/ammo_magazine/pellets = 4)