WooCommerce Smart Coupons 9.18.0

* Fix: Hitting button 'Enter' not adding product (created to sell store credit of any amount) to the cart
* Fix: Enabling the setting 'Combine Emails' doesn't have any effect. Coupons are not getting combined in email for the same user
* Update: Enqueue Smart Coupons CSS only if needed
* Update: POT file

* Fix: Notification for Bulk Generate > Export to CSV is not showing
* Fix: Admin Footer text not showing on Smart Coupons pages
* Update: Welcome page
* Update: POT file

* New: Tested upto WooCommerce 4.0
* Fix: PHP Warning: Invalid argument supplied for foreach
* Update: Setting to enable/disable feature to print coupons
* Update: POT file