OPENDJ-1116 Introduce abstraction for the changelog DB
Extracted interface org.opends.server.replication.server.changelog.api.ReplicationIterator from org.opends.server.replication.server.ReplicationIterator and used it in all the places where the class was used.
Renamed ReplicationIterator class to JEReplicationIterator.
Moved ReplicationIteratorComparator from package org.opends.server.replication.server to org.opends.server.replication.server.changelog.api.
MessageHandler.java:
Minimal code cleanup.