BibAuthorID: always create a profile, rabbit cleanup

* When reassigning signatures, to avoid huge
  concurrency problems by two users using
  the same author id in the same time, it is
  safer to always create a pid and clean up
  rabbit.
* Tuned remove_empty_authors to actually
  remove this authors.

Signed-off-by: Artem Tsikiridis <artem.tsikiridis@cern.ch>