OAK-593: Segment-based MK

Use AtomicReferences to track the latest head state

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1548354 13f79535-47bb-0310-9956-ffa450edef68
OAK-1266: SQL/JDBC DocumentStore implementation

Inline the json-simple library to avoid problems with OSGi

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1548355 13f79535-47bb-0310-9956-ffa450edef68