[ENH] Argument Variable 'page_no_namespace' added

As of now users have at their disposal the argument variable {{page}}, returning the complete page name. When working with namespaces however it could be desirable to retrieve the page name without the namespace. The argument variable {{page_no_namespace}} has been added in order to add this funcionality. Following the way things works as of now, for a page with title ending with the namespace separator, this new argument variable will return an empty string.