Loyalty discount order statuses selection by name rather than number.
Changed the order status database representation to a short string.
This makes it (somewhat) easier to:
-- import legacy orders with no-longer existing statuses (while still keeping some hint on what did they mean in the past);
-- add new statuses between existing ones, without migrating orders data;
-- write status logic clearly.
The first string in SHOP_ORDER_STATUS_CHOICES setting is meant to be an internal representation, potential values could be defined as constants. The second string is a human-readable representation (it may be marked for translation, even in settings).
Merge branch 'feature/string-order-statuses' into feature/loyalty-discounts