Update Forge to 10.12.0.1033. Refactor plugin custom entity support.

* Plugins now have the ability to use the CraftWorld.spawnEntity method to
spawn any custom entity. In order for this to work properly, MCPC+ will
inject all new EntityTypes into the Bukkit enum. Simply pass the custom
EntityType to CraftWorld.spawnEntity to spawn it.
* Removed most MCPC custom entity classes as they are no longer used.
* Merged latest fixes from MCPC v164 branch.