BibCheck: last_run correct update

• Correctly updates last_run information for each rule with the timestamp of the beginning of the execution of bibcheck rather than the end (thus avoiding loosing record updates happened during the execution of bibcheck itself).

• If filter_collection is not used in a rule, uses search_pattern() rather than perform_request_search() so that all records are considered and not only those that have been created/modified before the last webcoll execution.

Signed-off-by: Samuele Kaplun <samuele.kaplun@cern.ch>