Summary:
Ref T2787. This has some rough edges but basically works.
- Users can cancel orders that are in incomplete states (or in complete states, if the application allows them to -- for example, some future application might allow cancellation of billed-but-not-shipped orders).
- Merchant controllers can partially or fully refund orders from any state after payment.
Test Plan: This is still rough around the edges, but issued Stripe and WePay refunds.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: chad, epriestley
Maniphest Tasks: T2787
Differential Revision: https://secure.phabricator.com/D10664
