Reimplement Entities using Artemis

Glowstone can be unshackled by the stringent hierarchical system defined by Bukkit and begin to explore using the Artemis-ODB library for an Entity Component System. With this, we can safely loosen the Bukkit API and begin allowing plugins to generate their own customized Entities, enhance the Event API and overall, set the grounds for making Glowstone truly scaleable.

Links: 
Artemis ODB Wiki
https://github.com/junkdog/artemis-odb/wiki

Notes:
This PR depends on the Entities branch for importing the skeletal constructs that were supplied by said branch.

Ideas for the future:
The ECS branch will allow for easier AI implementation, customization of Entities and overall maintainability with Minecraft.