Implemented CMS storage for user and nodes.

Implemented role and permission storage.
Introduced the CMS_PARTIAL_NODE and CMS_PARTIAL_USER.
Added support for node storage extension
  - storage of data specific to each node content type,
  - in addition to the core CMS_NODE)
  - For now, only implemented for SQL storage.
Note: in current version, CMS_PAGE support is hard coded in the core,
    (as opposed to be only supported by the node module.)
Commented/removed for now, the Web API code to update node summary, title, via REST request.

library/persistence/implementation/store/cms_storage_store_sql.e

@@ -109,6 +109,11 @@ feature -- Query
 			db_handler.forth
 		end
 
+	sql_valid_item_index (a_index: INTEGER): BOOLEAN
+		do
+			Result := attached {DB_TUPLE} db_handler.item as l_item and then l_item.valid_index (a_index)
+		end
+
 	sql_item (a_index: INTEGER): detachable ANY
 		do
 			if attached {DB_TUPLE} db_handler.item as l_item and then l_item.count >= a_index then