Use I18NParentable interface duck-type check to determine whether a definition is i18n-ized

In BaseDialogPresenter class in order to avoid applying i18n magic multiple times we used to check if an incoming definition is a proxy (=> it was i18n-framework who's proxied an object).

However, such an assumption is not necessarily valid, especially since 5.4 (introduction of 'injectable' NamedDefinition interface via proxies) and 5.4.6 - definition decorators use proxies to provide fallbacks.

A safer way to determine that an object has been i18n-ized is to do an instanceof I18NParentable check.