BibField: fix copyright field names

* Fixes a typo for one of the copyright fields and also changes its name
  to `copyright_status` to avoid duplicate names.  (closes #1933)

Signed-off-by: Esteban J. G. Gabancho <esteban.gabancho@gmail.com>
Reviewed-by: Tibor Simko <tibor.simko@cern.ch>