YITH WooCommerce Account Funds Premium 2.5.0

* Update: Plugin Framework
* Update: Language files

* New: Support to WooCommerce 3.5.0 RC1
* New: Option to apply the coupon code to purchase funds
* Tweak: Add funds process
* Update: Plugin Framework
* Fix: Transaction history pagination issue

* Update: Plugin Framework
* Fix: Conversion issues during refund process using WooCommerce Multilingual