Add configurability for properties that should not be referenced in widgets

By default widget properties are wrapped to ensure a proper ajax refresh of widgets.
=> either rollback and see if it's still a problem now that layouts are properly rendered in ajax when the conf changes, either make properties that should not be wrapped configurable by widget type and mode or JSF component.

For now this is hardcoded in FaceletHandlerHelper#shouldCreateReferenceAttribute and does not care about the actual JSF component or widget type using it.