WooCommerce Checkout Add-Ons 2.7.4

* Fix - Handle inconsistent order item data to avoid Subscriptions renewal errors
* Fix - Allow "0" as a label for radio, select, checkbox group, or multi-select choices

* Fix - Ensure radio buttons can't be un-selected if used
* Fix - Ensure recurring add-ons are shown the Subscriptions "recurring totals" summary

* Fix - Ensure styles & scripts are loaded where needed when "WooCommerce" string is translated
* Fix - Ensure checkbox values are set properly as "yes" or "no" in order CSV exports
* Misc - Added support for WooCommerce 3.0
* Misc - Removed support for WooCommerce 2.4