Add ability to restrict payment methods on an invoice-by-invoice basis

Many credit card processors disallow accepting card payments for things such as remote tech support (i.e. helping someone with a tool like TeamViewer). It would be great if certain payment methods could be disabled automatically when a particular item is on an invoice, or if payment methods could be disabled on a per-invoice basis if that invoice contains any "banned" products or services. For example, my instance is configured with Stripe, BitPay, and PayPal. BitPay and PayPal don't restrict tech support billing, but Stripe does, and should not be an option when a customer is paying for tech support. This is also an issue with most other card processors, as it's a restriction imposed by Visa and MasterCard. I've talked at length with Stripe support, and the only reason they reversed a pending deletion of my merchant account is because I promised not to charge for tech support through their platform. They only gave me five days notice that my account…