BibCatalog: no newlines in subject for RT plugin

* Properly cleans any newlines from the given subject for the
  RT plugin as newlines are not accepted by the CLI bridge to RT.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
Reviewed-by: Samuele Kaplun <samuele.kaplun@cern.ch>