Forward port of checkpoint commit for OPENDJ-1471 File based changelog : improve cursor behavior

All cursors related to ReplicaDB now behave like java.sql.ResultSet API in JE implementation

(File based changelog implementation will be ported later)

* JEChangelogDB#getCursorFrom(DN, int, CSN) now returns a java.sql.ResultSet style cursor

* ChangeNumberIndex : advance cursor to first record to keep current behavior

* Update Javadoc in several classes : DBCursor,  ReplicationDomainDB, JEReplicaDB,
 JEReplicaDBCursor

* SequentialDBCursor (used in tests only) now behaves like java.sql.ResultSet API

* ChangeNumberIndexerTest : adapt to changes of SequentialDBCursor

* CompositeDBCursorTest : add more tests

* ReplicaOfflineCursorTest : adapt to changes of SequentialDBCursor