YARN-1633. Defined user-facing entity, entity-info and event objects related to Application Timeline feature. Contributed by Zhijie Shen.
svn merge -c 1563356 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1563357 13f79535-47bb-0310-9956-ffa450edef68