Fullscreen

Added a fullscreen button control, which changes the css of the OpenLayers map div to make it cover the full browser window. You can see it on my site e.g. http://www.wallandbinkley.com/rcb/omeka/items/show/101 - the button is the icon at the upper right. I think this really exploits the value of the zoomify approach by letting you get the deep zoom but not being limited to the small viewing window.