Implement Privat24 API

[ALEGATOR1209]

• Implement Privat24 API that fulfills our needs, in particular:
  • Receiving information about transactions (happened after some date);
  • Receiving information about user cards/accounts;
  • Receiving information about user balance.
  • Implement Bank DataSource

If Privat24 API doesn't support some of this requests, write it here or in Slack.

[ALEGATOR1209]

• Implement Bank DataSource