Sim Service

For now, some thoughts on the pool based sim service. It doesn't iterate every item. It doesn't keep a list of enabled and disabled items. Items can choose to be iterated or not. Sim service iterates every item that wants to be iterated each tick. Items should not be iterated if:

• They are static (unless specifically required)
• They are disabled
• They are enabled and do not have any observers or any code that needs to run each iteration.
• When in doubt, don't iterate it.

Sim service holds a reference to every realm that a simulated object is a member of. A local realm server does not need to be instantiated. Sim service will iterate the realm object if it needs to.