Revert "Revert "Authorize.Net: Switch to the XML API""

This reverts commit 0b8a0de2e2d547b96e0d1aac63d5ace8baf0e9ff.
Move customerIP to be below customer block in Authorize.net post_data XML
update eway validators
get tests passing
Parse multiple errors returned. Parse errors returned in 'ResponseCode' correctly
Merge pull request #1381 from Shopify/eway_rapide

update eway rapid validators
Merge pull request #1367 from Shopify/unrevert_authorize_net

Unrevert Authorize.net
Add order_id to Stripe metadata
Make a non_fractional_currency? accessor public
add test for public non_fractional_currency? accessor
Merge pull request #1390 from Shopify/fractional_currency_accessor

Make a non_fractional_currency? accessor public
Merge pull request #1388 from Shopify/stripe_metadata

Add order_id to Stripe metadata
Add Checkout.com

https://www.checkout.com/

Closes #1343.
HPS: Add verify support

Closes #1375.
Fix warnings in Eway Rapid tests
Add Bank Frick

http://www.bankfrickacquiring.com/

Closes #1380.
Add Global Transport gateway

https://www.globalpaymentsinc.com

Closes #1382.
iATS: Add #store and #unstore

Also removed stubbed out #authorize, #capture, and #void since they're
not supported and weren't functioning anyway.

Closes #1389.
Authorize.Net: Fix amount formatting

Truncate refId (order_id) to 20 characters to pass schema validation.

Closes #1393.
Authorize.net: Truncate more fields

Now we truncate more fields to fit within Authorize.net's requirements
and pass schema validation.

Closes #1394.