R1:eade206625ea

Introduce search result buckets

Summary:
Ref T10939. Currently, Differential hard-codes some behaviors for the "active" filter. This introduces "buckets" to make this grouping behavior more general/flexible.

The buckets don't actually do any grouping yet, this just gets rid of the `$query === 'active'` stuff so far.

These buckets change the page size to a large value, becuase pagination won't currently work with bucketing.

The problem is that we normally paginate by selecting one more result than we…