Update the navigation menu to have both 3.0.x and 2.3.x documentation available

git-svn-id: https://svn.apache.org/repos/asf/karaf/site/trunk@1553357 13f79535-47bb-0310-9956-ffa450edef68
Update the Karaf 3.0.0 documentation links

git-svn-id: https://svn.apache.org/repos/asf/karaf/site/trunk@1553358 13f79535-47bb-0310-9956-ffa450edef68