Add XOF (West African CFA Franc) to the currency list

XOF is the official currency of 8 West African countries in the UEMOA zone : Benin, Burkina Faso, Côte d'Ivoire, Guinea-Bissau, Mali, Niger, Senegal, and Togo covering over 130 million people. It is currently missing from Griply's currency list, making it impossible for users in this region to properly set up financial goals. Adding XOF would make Griply accessible to a large and growing market across francophone West Africa.