Add filter for default layered nav query type

Instead of hard coding the default query type to 'and', this would allow
us to filter it. This is definitely an edge case, but I'm building my
own layered nav widget that uses 'or' queries, and it's a bit of a pain
to have to specify `query_type_` parameters for every attribute.
Merge pull request #3011 from dominic-p/default-query-type

Add filter for default layered nav query type