Found and fixed a bug that had the potential to cause severe lag when entities were killed by fire.

Details:
HeadHunter must keep track of what player sets other entities on fire, so that it can drop their heads if they die from fire damage. This change also makes it so that fire damage caused more than one minute ago will not be attributed to the player that caused the fire damage. In most cases, fire damage will not last a full minute. This change is simply to limit any lasting impact HeadHunter has on the server's runtime.