OAK-1915: added images for documentation

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1628186 13f79535-47bb-0310-9956-ffa450edef68
OAK-1941 - add test for growing documents

git-svn-id: https://svn.apache.org/repos/asf/jackrabbit/oak/trunk@1628190 13f79535-47bb-0310-9956-ffa450edef68