Filtering currencies on refuel form

[magul]

AC1: Create CountryCurrency model in Django (in new Django application called configuration) with following fields:

• country
• currency
  AC2: Add available currencies list to current user serializer.
  AC3: Filter currencies in add refuel form based on current user available currencies.

[OtisRed]

Valid - waiting for model refuel (and frontend migrations) #481