Allow Breww to update a Sellar order's payment status

Currently, Breww just pulls payment information from Sellar. If an order comes through from Sellar to Breww as unpaid initially, and then a payment is added to Breww (either manually, or via an accounting integration), then this payment status is not pushed to Sellar. This feature request is to add support for pushing this payment status information to Sellar.

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