WooCommerce Shipping

From: https://github.com/Automattic/woocommerce-services/issues/970

There’s already a “Test print” button in the self-help page, but we need another one in the purchase dialog, because they serve 2 different use-cases:

* The merchant wants to make sure everything works while configuring the store (self-help page)
* The merchant wants to check everything works before giving us money (label purchase dialog)