This class implements the undo stack for Wonderlands. Every user action is added to the undo stack, and the user can then undo each action one at a time. This stack is intended to be "infinite" so that the user can always roll back to a safe state. In practice the stack is actually depth limited (to 100 actions), but the user can adjust this depth using the setMaxDepth: message.

	initialization
	initialize

	reset
	reset

	accessing	top
	closeStack Close the stack to prevent undoable items from being pushed onto it.
	getMaxDepth Returns the current maximum depth of the undo stack
	isEmpty Returns true if the undo stack is empty
	isOpen Returns true if the undo stack is open
	openStack Open the stack to allow undoable items to be pushed onto it.
	pop Takes the top undo action off the stack.
	popAndUndo Takes the top undo action off the stack and does it (undoing the original action).
	push: Pushes an undo action on the stack.
	setMaxDepth: Sets the current maximum depth of the undo stack
	top Return the top undo action off the stack.

	initialization	top
	initialize Initializes the undo stack.

	reset	top
	reset Reset the undo stack.

	instance creation	top
	new Create a new Wonderland undo stack and initializes it.