Fix OPENDJ-258: Integrate attribute cleanup plugin into OpenDJ (contributed by Profiq S.R.O)

Many thanks to Nemanja Lukic and his colleagues at Profiq S.R.O for this kind contribution.

The contribution has been modified as follows:

*) use the admin framework for validating the attribute renaming mapping
*) relax the constraint that attribute names must conform to RFC 4512 since non-compliant attribute names are good candidates for removing and renaming
*) modify the rename target attribute validation to support attribute descriptions
*) added schema element definitions for configuration attributes