Summary: Fixes T4610. Open to suggestions, etc., if there's anything I'm missing. Also: - Moves these "system" endpoints into a real application. - Makes `isUnlisted()` work a little more consistently. Test Plan: Accessed `/robots.txt`, `/status/` and `/debug/`. Reviewers: chad, btrahan Reviewed By: btrahan Subscribers: aran, epriestley Maniphest Tasks: T4610 Differential Revision: https://secure.phabricator.com/D8532