Set up DRF API for exchange app

[hexvolt]

Set up Django Rest Framework API for exchange application

[hexvolt]

Use cases for currency:

• [x] Get all currencies GET .../currencies/
• [x] Create/Update currency POST .../currencies/ PUT .../currencies/1/

Use cases for exchange_rate:

• [x] Create/Update exchange rate for certain bank POST .../exchanges_rates/ PUT .../exchange_rates/1/
• [x] Get all (or filtered by date) exchange rates for all (or certain) banks GET .../exchange_rates/?...
• • [x] Pagination
• • [x] Custom filter for getting the latest exchange rate for certain bank(s) and currency pair GET .../exhange_rates/?date=latest... Separate end point because most likely it will be used for various banks in a bulk, not necessarily for one bank only.

Use cases for conversion:

• [x] Create/Update a conversion POST .../conversions/ PUT .../conversions/1/
• [x] Get all (or filtered by date) conversions for certain currencies GET .../conversions/?...