Specify github for spree_gateway

[Fixes #2269]
Added BSD-3 license with copyright.

Copyright to Spree Commerce Inc. and other contributors.

Fixes #2274
[api] Allow a Rabl template to be specified during a request
Allow overriding of shipping method’s adjustment label

Fixes #2222
Fix tests broken by changes from #2222
Allow option values to be deleted from the admin backend

Fixes #2277
Test engines parallely with Travis

Closes #2267
Fix analytics_header override

Broken by a29eb288c64a2ab397e043c63332f050c5d41af4
Fix variant autocomplete now that rabl responses no longer have a root node
[promo] Ensure that an order has completed successfully in single use promotion test

Kind of a 'regression test' for this issue brought up by @daddeo2: https://github.com/spree/spree/commit/e9ad6c7a3deb107152a003bbbfc5d80947bb1832#commitcomment-2252676
Don't allow an order to transition to complete if payment is required and payments don't exist

Tentative fix for issue brought up here https://github.com/spree/spree/commit/e9ad6c7a3deb107152a003bbbfc5d80947bb1832#commitcomment-2252676
Simplify customer_details_spec autocomplete test's JavaScript

This is in an attempt to get that final core failing spec under control
Show add to cart if price in selected currency.

This is a bug with the cart form.  It would show the add to cart button
if there was a valid price in the master currency rather than the
current currency.  This causes the add to cart button to not display if
the product is not available in the master currency but available in a
different currency.

Fixes #2275
Guarding against Jirafe false positive conversions

Fixes #2273

Fixes #2211

Fixes #2157
Fix issue where product properties page was not displaying due to missing route

Fixes #2279
Fix issue where a blank credit card type would cause the order details page to complain about a missing asset

Fixes #2282
Only transition to complete if payment is required and there is a payments record OR if there is no payment required
Add taxon placeholder translation

Fixes #2288
Delete unused this_file_language translation
Refactor .travis.yml