Added EntityConstructed Event

This event is to be used to register any IExtendedEntityProperties
instances into the newly constructed entity.  It is placed in the
constructor so that it happens before the entity attempts to read from
NBT.
Added IExtendedEntityProperties

Extended Entity Properties allows a different approach than an NBT in
that one can have an instantiated class tied to the entity, allowing
methods and such to operate directly on the data without the need for
parsing from the NBT.
Added PotionBrewed Event

Event that will be thrown when a potion is brewed.
Added PlayerCreativeFall event
Revert "Added LivingInitEvent class to LivingEvent.java"

This reverts commit 9b4e045d12c926403bef2d29d121f706ea704e5e.
Adds functionality for the extended entity properties

Adds the actual collection (private), read/write NBT calls, a get method
and a register (set) method.
Adds a fall event when in Creative
Brewing stand changes and events

Changes the hardcoded lookup of Potion.itemID to instanceof ItemPotion,
which allows extended potions to be brewable.  Also adds an event when a
potion ingredient is applied.
Renamed PlayerCreativeFallEvent to PlayerFlyableFallEvent

more appropriate based on the code, as it doesn't just apply to
creative.