function addHoverState(elt)
			{
				mxEvent.addListener(elt, 'mouseenter', function()
				{
					elt.style.opacity = '1';
				});
				mxEvent.addListener(elt, 'mouseleave', function()
				{
					elt.style.opacity = '0.5';
				});
			}
Creates the buttons for the predefined styles.