OAK-50 : Implement User Management

- keep index when converting jcr user path

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1431959 13f79535-47bb-0310-9956-ffa450edef68
OAK-51 : Implement JCR Access Control Management (WIP)

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1431960 13f79535-47bb-0310-9956-ffa450edef68