(Libigot) Adds Block field referencing the beacon applying these potion effects

This expands this event's functionality adding a reference to the beacon block which could be used for a variety of applictions - for example determining the location of the beacon block to determine who to apply the beacon effects to (see Towny, Factions, Worldguard, Residence, etc).

An example of an application of this that was used to test this commit can be found at
    http://pastie.org/private/dvnmv59qlnkzxejrjmbzg