WebSearch: most popular field values optimisation
- Optimises get_most_popular_field_values(). Uses numpy.lexsort() when available. Improves time spent in Python. The bottleneck is now the database for searches giving more than 100000 results. (closes #1096)
- API change: get_most_popular_field_values() now returs list of tuples instead of tuple of tuples. The commit amends callers in WebAuthorProfile, BibKnowledge accordingly.
Co-authored-by: Tibor Simko <tibor.simko@cern.ch>