core, frontends: XMLUI refactoring: - XMLUI now use objects with 2 main classes: widgets (button, label, etc), and container which contain widgets according to a layout - widgets and containers classes are found through introspection, thereby it's really easy to add a new one - there is still the AddWidgetName helper, for example AddText('jid', 'test@example.net') will add a StringWidget with name "jid" and default value "test@example.net" - container can be inside other containers. changeContainer change the first parent container