OAK-150: Basic JCR LockManager support

Implement lock and unlock in NodeDelegate.
Trim the list of known locking issues.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1518045 13f79535-47bb-0310-9956-ffa450edef68
OAK-150: Basic JCR LockManager support

Only allow locking and unlocking of mix:lockable nodes

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1518046 13f79535-47bb-0310-9956-ffa450edef68