Small project intended to overview payment for AX services.
The association provides a number of base Products.
The price of such products evolves with time, as noted in ProductPrice objects.
On the other side, a member registers a PaymentMode (credit card, check, etc.);
money is then taken from his account through that payment mode, tracked in an Order.
A single PaymentMode can be used throughout the years, thus generating several Orders.
Each Order may be used to pay for one or more products, maybe not for the current user,
as recorded in a OrderItem.