Allow logged-out users to view the homepage

Summary: Fixes T3979. The content isn't necessarily very good yet (see T4103, T3583), but this makes it work (e.g., not be a login screen).

Test Plan: Loaded home as a logged-out user on a public install, saw home instead of login.

Reviewers: chad, btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3979

Differential Revision: https://secure.phabricator.com/D8075