Integrated crossbows/pneumatic cannons into launcher gun type, added back sprites.

Conflicts:
	code/modules/projectiles/gun.dm
	code/modules/projectiles/guns/alien.dm
	code/modules/projectiles/guns/projectile/crossbow.dm
	code/modules/projectiles/guns/projectile/pneumatic.dm
	icons/mob/back.dmi
	maps/tgstation2.dmm
Forgot dmi