observer progress, added to schema and added schema_observer class

include/matador/object/repository.hpp

@@ -67,8 +67,6 @@ public:
           return utils::failure(result.err());
       }
 
-      node->on_attach();
-
       foreign_node_completer<Type>::complete(node);
       relation_completer<Type>::complete(node);
     } else if (!has_node(name)) {
@@ -200,7 +198,7 @@ private:
 private:
   friend class internal::shadow_repository;
   friend class repository_node;
-  template < typename NodeType >
+  template < typename NodeType, template<typename> typename ...Observers >
   friend class foreign_node_completer;
   friend class object_generator;