As a client I should be able to disable/enable payment methods on backend and have it reflected on frontend

[ikorgik]

Problem

Falcon might have many different payment options in the future (PayPal, Stripe, Realex, etc). The end Falcon installation should work fine with any combinations of payment methods enabled.

Acceptance criteria

• As an admin, I can go to Donations backend and disable / enable payment methods (Stripe / PayPal so far).
• As an end user I should see only enabled payment methods on Gifts frontend
• As a developer I should not see any Javascript errors in console when either PayPal or Stripe payment method disabled.