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: Samuele Kaplun <samuele.kaplun@cern.ch>
Reviewed-by: Gilles Louppe <g.louppe@gmail.com>
Merge pull request #132 from kaplun/signature-reassignment-fix

BibAuthorID: single profile when moving signatures