Allow public to view transaction details

Summary: Fixes T6427.

Test Plan: Log out of sandbox, navigate to public task, click 'See Details' in a transaction. Get Dialog.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T6427

Differential Revision: https://secure.phabricator.com/D10759