Changes to the system
-You no longer combust at a specific stack number, stacks are seperate from being on fire
-New proc in living_defense.dm, that anything that adds fire_stacks should reference. Caps at -20 or +20 fire_stacks
-You can now resist when on fire to stun yourself and remove 5 fire stacks, if you hit 0 or get below it, you extinguish yourself
-Welders now ignite you, but don't add stacks, so if you previously had stacks from a source, and are hit with a lit welder, you will ignite
-Lasers add 5 stacks and ignite, so it becomes a "pseudo stun" ie: Do I want to stun myself or am I okay with running to something that can extinguish me
-Heat ray now adds 20 fire_stacks