Create woocommerce-uk_UA.po

Ukrainian language
Class name consistency for woocommerce_attributes > product_attributes. See #4019
Fix markup on form-pay.php

Payment method fields were not displaying on the "Checkout -> Pay" page
because checkout.js was using a input#payment_method_{name} selector, which
worked fine with the payment method markup used in the review-order.php template,
but not with the markup used in the form-pay.php template.

This moves the #payment_method_{name} attribute from the <li/> elements to the
<input/> element so that checkout.js correctly display's payment method fields.
Add WP JSON API Library
Fix strict standards warning
Add a custom trigger handler based on the value of select#field_to_edit
Modify WP_JSON_Server to allow authentication
Add required global functions for WP_JSON_Server class
Add REST API settings stub
Remove unused WP_JSON_Posts class
Add REST API endpoints/methods to WC API class
Add new /checkout/add-payment-method/ endpoint

Part of #3396
Add add_payment_method_action() handler

Part of #3396
Add form-add-payment-method.php
Fix up markup on form-add-payment-method.php

So that checkout.js correctly displays payment method's fields.
Part of #3396
Only display add_payment_method() when logged in

Part of #3396
Improve form-add-payment-method.php error & button

Part of #3396
Call add_payment_method_action()

Part of #3396
Redirect to My Account page after adding method

Part of #3396
Add a notice that payment method has been added

Part of #3396