columnview: Forward all focus to child

For the same reasoning as the preceding commit.

Also don't make GtkColumnView focusable. Its internal list view
is already focusable, which is enough to take care of the empty
view case.

gtk/gtkcolumnview.c

@@ -659,6 +659,8 @@ gtk_column_view_class_init (GtkColumnViewClass *klass)
   GObjectClass *gobject_class = G_OBJECT_CLASS (klass);
   gpointer iface;
 
+  widget_class->focus = gtk_widget_focus_child;
+  widget_class->grab_focus = gtk_widget_grab_focus_child;
   widget_class->measure = gtk_column_view_measure;
   widget_class->size_allocate = gtk_column_view_allocate;
 
@@ -1314,7 +1316,6 @@ gtk_column_view_init (GtkColumnView *self)
                           g_quark_from_static_string (I_("view")));
 
   gtk_widget_set_overflow (GTK_WIDGET (self), GTK_OVERFLOW_HIDDEN);
-  gtk_widget_set_focusable (GTK_WIDGET (self), TRUE);
 
   self->reorderable = TRUE;
 }