OAK-1138 Implement global per principal permission entry cache (wip)

- make EntryIterator even more lazy (avoid seekNext() in next())
- only cache 'everyone's entries globally

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1538870 13f79535-47bb-0310-9956-ffa450edef68