Added new grinding detection mechanics.

swapping between 2, or even 10 grinding locations will not result in the penalty being lifted
And if you use it enough, it gets registered as a server wide penalty zone so everyone that uses it gets the penalty.

Added a new Command to check special kills (/mh achievements) or(/mh kills)
Added a new Command to check if a zone is a known grinding spot (/mh checkgrinding) or (/mh isgrinding)

Fixed a NPE if killing using an enchanted diamond sword but not a full set of armour