Freeze basket on redirect and thaw on cancel
Submit the frozen basket within success view

This involves some trickyness with the templates as the default
preview.html wants to render the open basket (which is injected into the
template context via the basket middleware).  We duplicate some of the
basket template so we can render an alternative basket (the frozen one).

Conflicts:

	paypal/templates/paypal/express/preview.html
add COUNTRY to PayFlow API payload
(cherry picked from commit 1bbb556c85b5b938b97b542bb0f8c29a31f323bd)
add PAYPAL_NO_SHIPPING setting to disable shipping for PayPal Express

- create a new setting, PAYPAL_NO_SHIPPING (default: False)
- if PAYPAL_NO_SHIPPING is True, all PayPal Express transactions
  will omit shipping
- currently, the setting applies globally. If this module is used with
  physical goods in the future, it may be beneficial to revisit this
  change. Shipping charges should respond to the basket.is_shipping_required
  property, which will determine whether any of the included products
  require shipping.
Merge pull request #2 from mgmtech/patched_4x-basket-freeze

Patched 4x basket freeze