YITH WooCommerce MailChimp Premium 2.34.0

* New: support for WooCommerce 4.2
* Update: plugin framework
* Dev: added yith_wcmc_subscribe_on_completed filter
* Dev: added yith_wcmc_register_mailchimp_groups_registration_form filter
* Dev: added yith_wcmc_handle_checkout_manager_custom_fields filter

* New: support for WooCommerce 4.1
* Update: plugin framework
* Update: Italian language
* Tweak: improved WPML support for field placeholder translations
* Fix: prevent notice on advanced integration items
* Fix: prevent notice when printing "User preferences" metabox

* New: support for WordPress 5.4
* New: support for WooCommerce 4.0
* New: added Elementor widget
* Update: Spanish language
* Update: plugin framework
* Tweak: refactored store class to allow dev remove unwanted post_types from the sync
* Tweak: add privacy label to WPML config
* Fix: allow admin to pick up variations in advanced settings
* Fix: prevent notice when syncing cart on MC
* Dev: added yith_wcmc_supported_post_type_to_sync filter
* Dev: added filter yith_wcmc_process_item, to programmatically skip processing for some store items