[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 functionality. Following the way things work as of now, for a page having a title ending with the namespace separator this new argument variable returns an empty string.