Feature: Query authors and respondents #18

- Bugfix: Duplicated counts at aggregated levels (category, stream), due to the same message potentially being matched by multiple keywords.
- Update: Stream name is now queried directly from `display_recipient` field, rather than mapping from hard-coded `stream_id`.
- Update: Fields role -> thread.role, count -> thread.count
- Add: New output 'all messages' which is utilized by this feature.
- Update: Refactor to do with querying 'all messages' vs 'querying by keyword'.