Don't allow logged out users to initialize a Workboard

Summary: Right now logged out users can enable a workboard on a project.

Test Plan: Log out, view a public project, click on Workboard, get not set up dialog. Click Cancel, return to project details.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D14304