Added functions to find nodes in the scene graph. Also added functions to add scene nodes after the first initialization of the scene graph.

NOTES:
	+ The find functions all return pointers.
	+ The function in the class Scene will ensure the node is visible in the master node list, while the one in Scene node is only meant to be used by the aforementioned function and may cause errors if used by itself.

TODO:
	+ Add collision detection and physics
	+ Add particles
	+ Implement demo scripts
	+ LASERS!!!