WooCommerce Postcode Address Validation 2.11.3

* Fix - When using SmartyStreets and the current user reaching checkout has no saved billing/shipping address, an error could mangle the checkout process

* Fix - Fix postcode lookup in WC > 3.0
* Misc - Redefine ajax calls using custom WC ajax endpoints

* Fix - Patch Smarty Streets library issue that breaks state fields when only one country field is used at checkout
* Misc - Added support for WooCommerce 3.0
* Misc - Removed support for WooCommerce 2.4