Files - make file info page public

Summary: and for bonus, finesse some URIs a tad. Fixes T5922.

Test Plan: viewed F1 logged out and it worked! viewed the ugly URI for F1 and got redirected to the pretty URI.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5922

Differential Revision: https://secure.phabricator.com/D10309