Depend on Spree 2.1
Fix Linkpoint gateway to sum the discount and subtotal

* The Linkpoint gateway requires that the subtotal, tax and shipping
  equal the payment total. It completely ignores the discount
  provided, which could be the result of a promo code.

  This change adds the discount to the subtotal, and sets the
  discount to 0. While not strictly necessary to set to 0, I did not
  want to remove it completely since it breaks the contract already
  established that the gateway options include a discount key.

Fixes #103
Remove currency preference from Stripe Gateway

Use Spree::Config[:currency] instead
[stripe] Relying on incoming currency settings would be preferrable
Make always failing USA Epay spec as pending (for now)

This is truly a terrible gateway and nobody should use it.
Store both the customer id and payment profile id from Stripe

For #105