Properly support enableAjax() in WGLWidget
When progressive bootstrap is enabled, WGLWidgets will show the fallback if they are created on the initial page load. Ideally,
enableAjax() should be properly implemented to make sure they are rendered if possible.
Eventually, we should ideally eliminate all of the exceptions where progressive bootstrap does not work properly, see
examples/widgetgallery/approot/wt_config.xml for all of the exceptions in the widget gallery.
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