Add a Youtube widget

There are still some commits to come to get it to work with our new development environment,
namely that the plugin is being loaded from outside of the ckeditor plugins folder, such as updating `test.html`.
Maybe something like?

    getParam = function(element, param) {
        return element.attr('param') || element.attr('data-' + param);
    }

    url = getParam(embed, 'url') || "http://asdfajs"