Makes Fire Burn Again

Being lit on fire barely did anything, for multiple reasons, all which should be fixed in this PR.
First, the code to do damage based on bodytemperature was literally bugged and only applied the lowest level of damage, no matter what.
Second, wounds made autohealed them fairly fast, sometimes even outhealing the incoming damage.
Third, being on fire raised your temperature rather slowly.
Fourth, the lowest level of 'overheating' damage was rather low.

Changes:
The bodytemperature part of Life() is now unbroken and I accidentally fixed freezing not hurting, so yay.
Added a ten minute delay to wounds being able to autoheal them away.  Applying bandage/salves will skip this.
Temperature climb is now based on fire stacks while on fire, so more stacks means more and longer pain.
Lowest level of overheating was tweaked.
Running into people while on fire will split your fire stacks with them and light them on fire.
Port's /tg/'s on fire sprite.
Different mobs can have different icons for being on fire.
Bonus: Rejuv now removes pain.

code/modules/organs/wound.dm

@@ -85,10 +85,12 @@
 		return src.damage / src.amount
 
 	proc/can_autoheal()
+		if(is_treated())
+			return TRUE
 		if(src.wound_damage() <= autoheal_cutoff)
-			return 1
-
-		return is_treated()
+			if(created + 10 MINUTES > world.time) // Wounds don't autoheal for ten minutes if not bandaged.
+				return FALSE
+			return TRUE
 
 	// checks whether the wound has been appropriately treated
 	proc/is_treated()