YITH WooCommerce PDF Invoice 4.25.0

* Fix: hide Electronic Invoice options for vendors when the module is disabled
* Dev: new filter 'ywpi_vendor_options'

* New: support to WooCommerce 3.6.0 RC 1
* New: now, the credit notes are attached to the refund email when the order status change to refund
* Tweak: electronic invoice module (credit to Lorenzo Novia - webipedia.it)
* Update: Spanish language
* Update: Plugin Framework
* Update: updated mPDF library to the version 7.0
* Fix: replaced character € to prevent the file by Agenzia delle Entrate from being rejected (Electronic Invoice module for Italian customers)
* Fix: fixed the credit note formatted number
* Fix: billing receiver ID and PEc are not showed correctly
* Fix: Eletronic Invoice Fields not showed under billing section onside the checkout page
* Dev: deleted deprecated filter woocommerce_found_customer_details

New: create filename with a unique progressive ID (Electronic Invoice module for Italian customers)
Tweak: calculate unit price with approximation of 5 decimals (Electronic Invoice module for Italian customers)
Fix: tax calculation on order line items (Electronic Invoice module for Italian customers)
Fix: prevent errors with HTML special characters (Electronic Invoice module for Italian customers)
Fix: tax calculation on "Dati Riepilogo" in case of Product Bundle generated with WooCommerce Product Bundles (Electronic Invoice module for Italian customers)
Dev: added new font UnBatang_0613.ttf
Remove: admin notice for XML file name (Electronic Invoice module for Italian customers)