Ars magica coremod removal changes

Added a new method of storing data on entities as the NBTTagCompound didn't do what I needed.  Added getter, setter, save/load handlers, and the collection itself (private).

Added IExtendedEntityProperties interface.  This allows a different type of access to adding things to Entities, including methods and properties, as well as not needing any parsing or manual re-writing to the NBT when done, and removes a great deal of overhead for more complex additions.

Added events for a player falling when flight is enabled, when a potion is brewed, and when an entity constructed.  The last one is needed to be able to register your extended properties before the NBT read happens

Changed brewing to be able to accept modded potions (instanceof ItemPotion versus potion.itemID in the check)

These changes will remove the need for a CoreMod from Ars Magica.