More flexibility on the payment methods

A payment method is allowed on a given point of sale to pay a given order if:

1. It is allowed on the concerned point of sale
2. All products contained in the order have this payment method allowed (either directly or through its product family):
   • If a product associates NO payment methods, it inherits from Product family level
   • If a product associates to some payment methods, it overrides what has been configured at Product family level
   • If a product family associates NO payment methods, all payment methods are available for that product family (but restrictions may still be defined at product level)