Issue #2362517 by Wim Leers: Improve default 403/404 exception HTML subscriber: don't duplicate the page render pipeline, use the routing system — add system.403 and system.404 routes.
Issue #2349615 by mortendk | davidhernandez: Copy aggregator templates to Classy.
Issue #2349771 by lauriii | davidhernandez: Copy user templates to Classy.