GTK3: gtk_scrolled_window_add_with_viewport() is deprecated

gtk_scrolled_window_add_with_viewport has been deprecated since version 3.8 and should not be used in newly-written code.
gtk_container_add() will now automatically add a GtkViewport if the child doesn’t implement GtkScrollable.
https://developer.gnome.org/gtk3/stable/GtkScrolledWindow.html#gtk-scrolled-window-add-with-viewport