Summary:
Ref T2787. Make this a little more concrete with explicit membership instead of a general edit policy. In particular, we need to know who to email when orders happen, and can't reasonably do that with an edit policy.
I imagine this might eventually get more nuanced (e.g., users who can only approve orders vs users who can manage the merchant itself) but that's a long ways away.
Test Plan: {F216284}
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Maniphest Tasks: T2787
Differential Revision: https://secure.phabricator.com/D10681
