Add child page support.

- Add support to create a new node as a child of an existing node.
   - Update or add a parent for a given node.
Fix delete and trash behavior: when a node is not published only the
   - author or admin see it.

Fix Node and Page node Revisions.

modules/node/persistence/cms_node_storage_i.e

@@ -117,6 +117,11 @@ feature -- Access
 		deferred
 		end
 
+	available_parents_for_node (a_node: CMS_NODE): LIST [CMS_NODE]
+			-- Given the node `a_node', return the list of possible parent nodes id
+		deferred
+		end
+
 feature -- Change: Node
 
 	save_node (a_node: CMS_NODE)