Refactor Cardano off-chain code

[vlasin]

Our goal is to transition from bash scripts to a proper backend framework. We need to unify separate bash scripts and Haskell backend code into a single workflow with different functions implementing off-chain code for different types of scripts that we have. See also #35.

• Investigate the viability of using Atlas.
• Refactor backends #55
• Refactor E2E tests #56
• Add E2E tests to CI #57
• Replace transaction building code with the Atlas API. #66

[zlonast]

I think cardano-submit-api is also an option if we want to remove bash scripts.

Setting this up for testing and for actual use on a real network.