Updated table nodes to support soft deletes using the new field

'deleted_at' as Datetime and give us free metadata.
Updated Sqlite builder to test different scenarios for users and roles.
Updated NODE_FORM_RESPONSE.edit_form feature to add a delete operation iff
there is a node ie node id >0 and the current user has delete permission on it.
Updated NODE_HANDLER.do_post to handle the operation "DELETE".
Updated queries to retrieve nodes filter by no logical deleted rows (ie. deleted_at is NULL).
Updated CMS_USER_API.has_permissions. (authenticated_user_role seems to generic).

examples/demo/site/scripts/node.sql

@@ -11,7 +11,8 @@ CREATE TABLE "nodes"(
   "author" INTEGER,
   "publish" DATETIME,
   "created" DATETIME NOT NULL,
-  "changed" DATETIME NOT NULL
+  "changed" DATETIME NOT NULL,
+  "deleted_at" DATETIME NULL
 );
 
 CREATE TABLE page_nodes(