YITH Stripe Connect for WooCommerce Premium 2.40.0

* New: support for WordPress 5.4
* New: support for WooCommerce 4.0
* New: support for API 2020-03-02
* Update: Stripe PHP library to version 7.27.2
* Update: plugin framework
* Update: Dutch language
* Tweak: improved check over WooCommerce existance
* Tweak: idempotency key now is generated basing on order id
* Tweak: code refactor
* Dev: added new function to get charge object
* Dev: added new function to get balance transaction object

* 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