st-widget: Copy get_focus_chain and navigate_focus from StContainer

We can't get rid of the implementations in StContainer just yet,
as StContainer still keeps its own child list. But this should
lower the amount of code that has to be moved around when we
remove StContainer.

https://bugzilla.gnome.org/show_bug.cgi?id=670034

src/st/st-widget.h

@@ -86,6 +86,8 @@ struct _StWidgetClass
                                     ClutterActor     *from,
                                     GtkDirectionType  direction);
   GType    (* get_accessible_type) (void);
+
+  GList *  (* get_focus_chain)     (StWidget         *widget);
 };
 
 GType st_widget_get_type (void) G_GNUC_CONST;
@@ -151,6 +153,9 @@ void                  st_widget_style_changed             (StWidget        *widg
 StThemeNode *         st_widget_get_theme_node            (StWidget        *widget);
 StThemeNode *         st_widget_peek_theme_node           (StWidget        *widget);
 
+GList *               st_widget_get_focus_chain           (StWidget        *widget);
+
+
 /* debug methods */
 char  *st_describe_actor       (ClutterActor *actor);
 void   st_set_slow_down_factor (gfloat factor);