Custom menu links may use URLs that are not covered by the client
router. When following a link that shares the domain, it will be
intercepted by the catchall route and a visual 404 will be mistakenly
shown. With this change, all of the custom links in this menu are marked
as external so that following them causes a full reload and a 404 is
shown only in the appropriate case.
Change-Id: I1cad36de97786a0f9af42e08105ab485fa198a15
660e180e4e