DMAP-27 - Fallback from alternate link to device group specific url not working

* allow fallback to device group url or to selectors based url if no alternate link exists for current detected device group

git-svn-id: https://svn.apache.org/repos/asf/incubator/devicemap/trunk/browsermap/trunk@1507787 13f79535-47bb-0310-9956-ffa450edef68