unused imports
let drilldown_map be any iterable
CasePaginator changes

- Change default sort to modified_on desc instead of asc
- add sort parameters
- refactor {"or": [{"term": {"owner_id": "..."}}, {"term": {"owner_id": "..."}}...]}
  es queries to {"terms": {"owner_id": ["...", "..."]}}
- allow to take an addition filter parameter, and let CaseListMixin subclasses
  implement the case_filter attribute to provide that