Provide a default sort for browse-linked result pages

[Mike Rylander]

Sorting the search result of records linked from a browse currently simply sorts on pubdate (the ultimate fallback). In some contexts it would make sense to sort by something else. For instance, results derived from a subject browse could default to a title or author sort.

Because browse is basically a per-search-class thing (though, not strictly -- one could construct a cross-class axis), providing a default_sort column on config.search_class or the authority axis definition table, and using that when building result links in browse seems like a relatively low-effort solution.