Integrated with CryptoCompare API

[Tibo-lg]

For the first version we will get data from the cryptocompare API.

Objectives

• Implement a client to the cryptocompare API.
• Use the client to retrieve data and sign it when first requested.
• Add unit and integration tests (might not be a good idea to use the actual cryptocompare api even for integration tests).

Technical considerations

• It might be cleaner to put the API client in a separate repository for reusability/separation of concern.
• The integration should be done through dependency injection so that it will be easy to integrate other data feeds in the future. This means defining a DataProvider interface and implementing it using the cryptocompare client. "Static dependency injection" (instantiated in the main) should be enough for now.
• A private key will be required to produce signatures, this should be given to the application see this for some recommendation. As a first step putting it in a config file could be enough.