Barcelona sprint financials

I'm creating this issue to document & track the discussions we had at the Barcelona sprint.

We had a financial team of @mattwire @JoeMurray @ayduns @artfulrobot @BjoernE @andrei @ejegg present

Main issues

1. Ensuring there were no blockers to people using the Order.create->PaymentProcessor.pay->Payment.create flow #76
2. Making the poor performance associated with the creditnote_id field opt in rather than opt out #84 (closed)
3. Addressing Stripe's need to store some Stripe generated information for which there is no suitable field. We resolved this at the data level by adding the field civicrm_financial_trxn.result_code. However docs pending! #57
4. Having a plan to get off our broken contribution.template model #6 (closed)
5. UI for permitting refunds processing for payments. #85

Not actually from the sprint but topical from discussions - add getters & setters to payment processor base class #82