matcher: Python 3 compatability

* Using six library for cross-python compatability.

* Exceptions included for unimplemented features in
  the CLI.

Co-authored-by: Jan Åge Lavik <jan.age.lavik@cern.ch>

Signed-off-by: Graham R. Armstrong <graham.richard.armstrong@cern.ch>
matcher: Review changes, legacy code deletion

* Legacy BibMatch module removed as it's no longer used.

Reported-by: Jiri Kuncar <jiri.kuncar@cern.ch>
Co-authored-by: Jan Åge Lavik <jan.age.lavik@cern.ch>

Signed-off-by: Graham R. Armstrong <graham.richard.armstrong@cern.ch>