[HTMLEditor] need focused states when a child really has focus

HTMLEditor need to be styled so that it paints a focus border when the WebView really the focus owner. The idea is to add a new pseudo class state called "focused-child" or similar which will be added to the control by the skin and maintained by the skin. It will be bound to the focused state of the key child. Once this is done the CSS can be updated to draw focus correctly for these controls.