Restrict Workboard initialization to CAN_EDIT
Summary: Make Workboard initialization more restrictive.
Test Plan: Log out, see "No Workboard", Log in with permissions, see "New Workboard", Log in with notchad, see "No Workboard".
Reviewed By: epriestley
Maniphest Tasks: T7410
Differential Revision: https://secure.phabricator.com/D14306