OAK-633: SegmentMK: Hierarchy of journals

Drop this feature for now as we won't have time to complete it
before Oak 1.0 / Jackrabbit 3.0, and keeping it around complicates
other work.

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1575327 13f79535-47bb-0310-9956-ffa450edef68