browser side (XMLUI): XMLUI update to follow core changes: - Dialogs are now managed - FileDialog raise a NotImplementedError, it's not yet possible in Libervia - XMLUIPanel.show is implemented - following core changes, we now create an XMLUI with xmlui.create(...) - WidgetFactory now inherit from GenericFactory - workaround for __getattr__ bug in pyjamas, now createXXX are automaticaly created with inspection