YITH WooCommerce PDF Invoice 4.25.0

* New: Support for WooCommerce 4.5
* New: Integration with YITH Frontend Manager for WooCommerce
* Update: plugin framework
* Update: language files
* Fix: fixed fatal error
* Fix: avoid displaying credit note documents in orders in My Account page if option is not enabled
* Dev: changes in the credit note with products
* Dev: added new filter yith_ywpi_validate_checkout_fields_conditions
* Dev: improved the credit note
* Dev: remove the precision in the credit note % tax
* Dev: convert state code and convert it to the state name
* Dev: optional label on checkout can be now translated
* Dev: added new filter ywpi_checkout_optional_label

* New: Support for WooCommerce 4.4
* New: Support for WordPress 5.5
* Tweak: make mandatory ssn only for invoices when electronic module is enabled (Italian Customers)
* Update: plugin-fw
* Fix: avoid display array and object meta values in product variations
* Fix: required ssn rule
* Fix: show phone field only if customer has a phone number associated (electronic invoice)
* Dev: replaced deprecated method get_product_from_item
* Dev: changes in the increment invoice number method
* Dev: added the gift card discount as negative

* New: Support for WooCommerce 4.3
* Tweak: validate SSN field only for private customers (Electronic Invoice)
* Update: plugin-fw
* Update: language files
* Fix: fixed displayed warnings in the plugin settings
* Fix: ssn error message showed always
* Dev: added new filter yith_ywpi_ssn_field_placeholder
* Dev: added new filter yith_ywpi_vat_field_placeholder
* Dev: changes the fee tax precision
* Dev: added new filter ywpi_invoice_information_url
* Dev: added new filter ywpi_dropbox_folder
* Dev: added the extension param in some functions