OAK-633: SegmentMK: Hierarchy of journals

Use a more aggressive merge strategy to prevent conflict markers from showing up

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1453786 13f79535-47bb-0310-9956-ffa450edef68
OAK-641: Improved benchmark tooling

Add some large-scale read benchmarks

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1453787 13f79535-47bb-0310-9956-ffa450edef68