Paypal Express gateway: Add unstore support

The #store method creates a billing agreement. Now the #unstore method
cancels a billing agreement.

Closes #716.
Stripe: Send application_fee with capture requests.
Merge pull request #714 from Shopify/payflow-fix

Use just name instead of firstname & lastname.
Merge pull request #718 from Shopify/stripe-application-fee

Stripe: Send application_fee with capture requests.
for bluepay gateway name1 & name2 should be populated from the payment method
Make #unstore method interface more consistent

While it's true that a number of gateways don't use the options
parameter in their #unstore method, having that parameter there with a
default value allows consumers of the API to call the method
consistently regardless of the gateway.

Closes #721.
fixed signature calculation method

and improved signature verification testing
fixed notification test check
don't verify signature if checkout failure
tests now use real callback and redirect data

also renamed test objects for clarity
Merge remote-tracking branch 'upstream/master'

Conflicts:
	lib/active_merchant/billing/integrations/dwolla.rb
	lib/active_merchant/billing/integrations/dwolla/common.rb
	lib/active_merchant/billing/integrations/dwolla/helper.rb
	lib/active_merchant/billing/integrations/dwolla/notification.rb
	lib/active_merchant/billing/integrations/dwolla/return.rb
	test/unit/integrations/dwolla_module_test.rb
	test/unit/integrations/helpers/dwolla_helper_test.rb
	test/unit/integrations/notifications/dwolla_notification_test.rb
	test/unit/integrations/returns/dwolla_return_test.rb
Remove unneeded require.
Stripe: Include swipe_data parameter if provided.
Use track_data instead of swipe_data on the AM side.
Include a track_data attribute on the credit card class.
Update test credit card information for banwire.
Add test for visa card.
Fix outdated error message from banwire.
Merge pull request #720 from cagerton/fixing_name_for_bluepay

bluepay gateway add_address was overwriting the name fields
Merge pull request #733 from Shopify/banwire-test-fix

Banwire tests fix