Reads the mouse and/or keyboard data sent from a
GraphicsWindow, and transmits it down the data graph.
The mouse and keyboard devices are bundled together into one device here, because they interrelate so much. A mouse might be constrained by the holding down of the shift key, for instance, or the clicking of the mouse button might be handled in much the same way as a keyboard key.
Mouse data is sent down the data graph as an x,y position as well as the set of buttons currently being held down; keyboard data is sent down as a set of keypress events in an EventDataTransition. To throw these events to the system, you must attach an EventThrower to the MouseAndKeyboard object; otherwise, the events will be discarded.