v1.0 - IEntity protocol

[DougHamil]

Replace the defcomponent macro with IEntity protocol.

The IEntity protocol allows users to register custom entities with threeagent. IEntity implementations will then be passed in to the threeagent.core/render function as a map, in the same manner as ISystem. This should provide a more consistent dev experience, and allows for more flexibility in defining new types of entities.

The protocol should have these methods:

• create - creates an instance of this entity type, which should be a ThreeJS object
• destroy - destroys an instance of this entity type
• update - does an in-place update of an instance of this entity type, provided the original ThreeJS object and updated parameters

All built-in defcomponent should be replaced with this protocol.