BibAuthorID: single profile when moving signatures

* Attributes signatures re-assigned by a curator
  to a single profile. So far, one new pid was
  created per paper.

Signed-off-by: Artem Tsikiridis <artem.tsikiridis@cern.ch>
Reviewed-by: Gilles Louppe <gilles.louppe@cern.ch>
Merge pull request #122 from atsikiridis/signature-reassignment-fix

BibAuthorID: single profile when moving signatures