Reduce weighting of fallback match_all_terms clause
Reduce weighting of fallback match_all_terms clause

As we have a bunch of single-field match_all_terms clauses, this final
one will only match if the terms are all present but spread across
different fields.  That's better than not matching, but it's not a
very strong indication of relevance compared to other factors.

alphagov/rummager,alphagov/rummager