OAK-91 : Implement Authentication Support 

- make all token related properties protected (-> drop nt:unstructured super type)
- allow for individual expiration time being passed by app overriding the configured default expiration time

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1508330 13f79535-47bb-0310-9956-ffa450edef68