Add the ability to be damaged by players (melee)

This PR adds the ability for players to be melee attacked by other players. This does not handle things like potions, arrows, etc. Specified non-standard weapons are damaged upon impact as well.

Included is a mapping of item type to damage "force". The same utility class can also critical hits for whoever the poor soul that does that is. 

Some additional utility methods were added for future support beyond damage, but they are directly used by this PR. 
As-is is probably fine in this case.