BibSort: enable sorting buckets for demo site

• Enable several bibsort methods for the demo site

• Enable the use of bibsort buckets for ranking in the search_engine.py

• Bibsort buckets for ranking to contain the actual ranking scores, and not bibsort weights, in order to display them to the user.

• Use sort_records_bibxxx() when sort_pattern is present since bibsort can not handle this parameter yet.

• Fix failing regression tests.