OPENDJ-1116 Introduce abstraction for the changelog DB
Renamed some classes in package src.server.org.opends.server.replication.server.changelog.je:
- DbHandler.java => JEReplicaDB.java (and tests)
- DraftCNDbHandler.java => JEChangeNumberIndexDB.java (and tests)
- DraftCNDbIterator.java => JEChangeNumberIndexDBCursor.java
*.java:
Consequence of the renames.
Changed methods/variables/parameter names and comments to reflect the new names. In particular, bye bye to DraftCNDb, DbHandler and welcome to CNIndexDB and ReplicaDB.