WooCommerce Newsletter Subscription 4.1.1

* Tweak - Fetch only the necessary fields when getting the Mailchimp lists.
* Tweak - Get all Mailchimp lists instead of only the first 10 lists.
* Tweak - Tested compatibility with WC 5.4

* Feature - Refresh the provider lists on the settings page.
* Feature - Refresh the subscription stats in the dashboard widget.
* Tweak - Tested compatibility up to WC 5.3.

* Feature - New provider: MailerLite.
* Feature - New provider: MailPoet 3.
* Feature - New provider: SendGrid.
* Feature - Subscribe customers only on specific order statuses.
* Tweak - Validate the provider credentials before connecting the store.
* Tweak - Check the plugin required by a provider is installed. E.g. MailPoet.
* Tweak - Updated recommended privacy policy texts.
* Tweak - Better error handling for the subscription widget.
* Tweak - Check the minimum requirements before initializing the plugin.
* Tweak - Tested compatibility with WC 5.1.
* Tweak - Tested compatibility with WP 5.7.
* Fix - Fixed MailPoet 2 stats when the 'Signup' confirmation' option is enabled.
* Dev - Revamped the integration with the different providers.
* Dev - Log possible errors thrown by the providers' API requests.
* Dev - Replaced the Campaign Monitor PHP client by the WordPress HTTP Request API.
* Dev - Updated the minimum requirements to WC 3.0, WP 4.4, and PHP 5.4