Import refund data from CSV

Authored by Ejegg.


Import refund data from CSV

New command drush import-refunds processor filename takes a CSV file
with the gateway's original order ID, refund date, currency, amount,
and optionally the gateway's refund ID and refund type, and marks
each as refunded.

Heavily modified version of old import_chargebacks.
TODO: maybe try/catch on each line?

Bug: T110367

Change-Id: I3cc58e7b8561a4a589091497de6ad82ea38bc11f