R1:a8bc87578e94

Clean up rendering of credit card form

Summary:
General cleanup and separation into generic vs Stripe blocks of code.

- There was an old CC form view for Stripe stuff that I never cleaned up; clean that up.
- Move non-Stripe CC form rendering into a base class (Balanced can reuse it).
- Move non-Stripe CC form JS into a shareable class.
- Simplify JS a bit (JX.Workflow can add extra parameters to a request, so we don't need hidden inputs).
- Genericize CSS.
- Depend on Stripe JS directly, if…