Stripe Refunds Integration

Here it is! Refund support for purchases. It was super easy to implement. No subscription refunds just yet. I figure this would be worked in a later time. Let me know what you think. I'd like to pull this in as soon as possible because I'm using it for a project.

Also, there is this other pull request I wanted to do regarding the payment method title because it somewhat affects this but only on a front-end sort of way.