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
Wrap GtkSettings new properties as of 3.12

* GtkSettings::gtk-decoration-layout property
* GtkSettings::gtk-shell-shows-desktop property
* GtkSettings::gtk-dialogs-use-header property