Checkpoint commit for OPENDJ-1206 : Create a new ReplicationBackend/ChangelogBackend to support cn=changelog

Merged + corrected backend error messages by passing in the backendID into the error messages + fixed translations (!?!)
Started implementing ChangelogBackend by adding error messages.
Used Collections.emptySet() for supported controls and / or features, where applicable.
Generecized Backend class with the type of the configuration object + applied specific types to sub-classes of Backend.
Code cleanups + factorized code by extracting methods + ran AutoRefactor.