Woocommerce Amazon S3 Storage 2.7.1

* Feature - Added wizard to add and edit the S3 files of a downloadable product.
* Tweak - Declare compatibility with WooCommerce High-Performance Order Storage (HPOS).
* Tweak - Tested compatibility with WC 7.1.
* Tweak - Tested compatibility with WP 6.1.
* Dev - Dropped deprecated template 'settings.php'.

* Feature - Added settings for defining the default bucket and region.
* Tweak - Added new S3 regions to the list.
* Tweak - The shortcode parameter 'bucket' is now optional.
* Tweak - Use the shortcode name to contextualize the filters when parsing the shortcode parameters.
* Tweak - Tested compatibility with WC 7.0.
* Fix - Fixed "Unrecognized S3 region" log message for valid regions that weren't on the list.

* Tweak - Moved the plugin settings to an integration page.
* Tweak - Updated text-domain of the translatable strings to 'woocommerce-amazon-s3-storage'.
* Tweak - Added missing descriptions to the translatable strings.
* Tweak - Check the minimum requirements before initializing the plugin.
* Tweak - Moved the 'Docs' and 'Support' links to the plugin row links.
* Dev - Deprecated 'settings.php' template.
* Dev - Deprecated code from the legacy setting for disabling SSL.
* Dev - Implement the singleton pattern in the main plugin class.
* Dev - Updated the minimum requirements to WC 3.4, WP 4.7, and PHP 5.4.