Get Cybersource remote tests passing 100%

Re-ordered setup fee to match XSD, and removed
test_successful_tax_calculation_with_nexus since ActiveMerchant cannot
and should not test the specifics of how Cybersource calculates taxes.
Cybersource: Add a test for monthly options

Closes #918.
Stripe /cards endpoint does not update a customer.
Replace hard-coded years with values based on the credit card expiration year.
Merge pull request #974 from boone/fix_tests

Fix tests.
Add back Stripe's refund_application_fee parameter to the refund method
Add failing tests
Merge pull request #971 from michellebu/master

Stripe /cards endpoint does not update a customer.
Merge pull request #981 from Shopify/stripe_add_refund_application_fee_back

Add back Stripe's refund_application_fee parameter to the refund method
Allow passing in the Stripe API version as an initialiation option
Added all non-fractional currencies
Merge pull request #982 from Shopify/stripe_version_initialization_argument

Allow passing in the Stripe API version as an initialiation option
Update CHANGELOG
Bump version to 1.42.4
Merge pull request #983 from Shopify/add_all_non_fractional_currencies

Added all non-fractional currencies
Updating helper to match current 2Checkout parameters.

-Remove 'fixed' as it is no longer used.
-Make 'merchant_order_id' the order identifier and make cart_order_id
optional as it is only used with the legacy third party cart parameter
set.
-Rename 'auto_settle' to 'third_party_cart' to identify the parameter
set being used. Pass Through Products parameter sales also automatically
settle now so the 'auto_settle' method name is confusing.
-Add mapping for currency through the new `currency_code` parameter.
Use notification to handle INS messages

notification should be reserved to handle 2checkout INS messages
all INS messages are live (not sent on demo sales)
move previous notification logic to return

return should be used to handle the initial passback from 2Checkout
tests cover demo and live sales
add coverage for the extra helper fields
return_url mapping to x_receipt_link_url parameter