enabled Audit to filter Concern vs. No-Concern status

Summary:
Fixes T2582

You can filter Concern vs. No-Concern status

Choosing a concern filter that's not `all` implies filter `status` to be `open`

Test Plan: fiddled around with it in Audit

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2582

Differential Revision: https://secure.phabricator.com/D5140