YITH Stripe Connect for WooCommerce Premium 2.31.0

* New: support for WordPress 5.3
* New: support for WooCommerce 3.8
* New: support for 2019-11-05 API
* Update: Plugin framework
* Update: StripePHP library
* Fix: notice when registering failed payment attempt
* Fix: deprecated function called on verify_intent error handling
* Dev: added new parameter to yith_wcsc_create_commission filter

* Tweak: minified checkout js
* Tweak: reviewed renew_needs_action subject to remove HTML string
* Tweak: moved methods to set card as default and delete card from gateway to main class
* Tweak: changed conditions that triggers renew_needs_action email sending, to be more specific
* Tweak: after registering failed renew attempt, get order again to account for any status change
* Update: Italian language
* Update: Dutch language
* Fix: fixed language files name
* Fix: payment intent missing customer for guest users

* New: support for SCA-ready payment methods
* New: extended card management, even without YITH WooCommerce Subscription enabled
* New: renew needs payment email (only when used with YITH WooCommerce Subscription)
* New: support for 2019-09-09 API version
* Update: internal plugin framework
* Update: Stripe PHP to version 7.0.2
* Update: Italian language
* Fix: avoiding duplicated connection attempts
* Dev: added new action 'yith_wcsc_after_disconnect_with_stripe' after user disconnect from Stripe
* Dev: filter yith_wcsc_disconnect_from_stripe_button_text and filter yith_wcsc_connect_with_stripe_button_text