MouseClickState is a simple class managing the distinction between clicks, double clicks, and drag operations. It has been factored out of HandMorph due to the many instVars.

Instance variables:
clickClient <Morph> The client wishing to receive #click:, #dblClick:, or #drag messages
clickState <Symbol> The internal state of handling the last event (#firstClickDown, #firstClickUp, #firstClickTimedOut)
firstClickDown <MorphicEvent> The #mouseDown event after which the client wished to receive #click: or similar messages
firstClickUp <MorphicEvent> The first mouse up event which came in before the double click time out was exceeded (it is sent if there is a timout after the first mouse up event occured)
firstClickTime <Integer> The millisecond clock value of the first event
clickSelector <Symbol> The selector to use for sending #click: messages
dblClickSelector <Symbol> The selector to use for sending #doubleClick: messages
dblClickTime <Integer> Timout in milliseconds for a double click operation
dragSelector <Symbol> The selector to use for sending #drag: messages
dragThreshold <Integer> Threshold used for determining if a #drag: message is sent (pixels!)

	initialize
	client:click:dblClick:dblClickTime:dblClickTimeout:drag:threshold:event:

	event handling	top
	click
	doubleClick
	doubleClickTimeout
	drag:
	handleEvent:from: Process the given mouse event to detect a click, double-click, or drag. Return true if the event should be processed by the sender, false if it shouldn't. NOTE: This method heavily relies on getting *all* mouse button events.

	initialize	top
	client:click:dblClick:dblClickTime:dblClickTimeout:drag:threshold:event: