Wrap new GtkStack symbols as for 3.12
Wrap new GtkStack symbols as for 3.12

* gtk_stack_get_transition_running function
* gtk_stack_get_child_by_name function
* GtkStack::transition-running object property

johne53/MB3Gtkmm,johne53/MB3Gtkmm,GNOME/gtkmm,GNOME/gtkmm,GNOME/gtkmm,GNOME/gtkmm,johne53/MB3Gtkmm