Handle adding children to StTable from Javascript

Remove the StTable specific methods to add actors:

 st_table_add_actor()
 st_table_add_actor_with_properties()

Since they shadow the generic ClutterContainer add_actor() method,
and patch in our add() convenience function as we do for
StBoxLayout.

https://bugzilla.gnome.org/show_bug.cgi?id=596811

js/ui/environment.js

@@ -26,6 +26,7 @@ function _patchContainerClass(containerClass) {
 }
 
 _patchContainerClass(St.BoxLayout);
+_patchContainerClass(St.Table);
 
 function init() {
     Tweener.init();