Changes to the demo browser to support a different zoom mechanism and relayout when settings are changed.
Custom mark images now scale by the dots per pixel property.
Changing the default font metrics property clears the text measurement cache.
Added resetBoxAndLayout() method to RootPanel that clears all calculated Box and Layout information.
Added more zoom options to demo browser.
Demo browser now zooms by changing the DPI and Dots Per Pixel settings.
Removed references to ScalableXHTMLPanel in demo browser.