payout via ACH

[chadwhitacre]

#3366 unraveled but the dream is still alive! Blocked on

Some good background: http://www.programmableweb.com/news/ordering-%E2%80%9Csecret-menu%E2%80%9D-ach-payment-platforms/analysis/2016/02/16.

Payin is #777.

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[nobodxbodon]

Re-ticketed to gratipay/inside.gratipay.com#974 for further discussion and planning. After deciding on concrete implementation plan and dev work starts, this will be reopened for tracking purpose.