A little clean-up for InchCoord's cluster stuff

• Made isClusterBaseClass and isClusterSubClass into class methods, like SceneViewController.
• Made raiseNotImplementedInClusterClassExceptionForMethod: instance and class methods from raiseNotImplementedInClusterClassException() function, also like SceneViewController.
	• Messages improved a bit too.
• Documentation comments here and there.
• Some more stuff listed in InchCoord's internal @interface.
• Moved things (sInchCoordStandIn, all the function->methods) around a bit.