Implement Plaid's Processor Token Endpoint (non-Stripe Specific)

[joeblas]

Plaid now has an additional processor token endpoint for other integrations besides Stripe. The documentation is here.

Should be a straightforward implementation. I may even take a stab at it.

[Ackara]

when I get the chance

[NicholasBrockman]

@Ackara would you mind if I created a PR to address this? We are using plaid for one of our integrations and are not using stripe, so this would be helpful.

[viceroypenguin]

@NicholasBrockman - if you need this quickly, please feel free to checkout viceroypenguin/Going.Plaid. I am keeping it up to date according to their public API spec, so it should include these endpoints. Specifically, the code is present here and here.