Shelley Modelling

[Sam-Jeston]

With the release of: https://github.com/input-output-hk/js-chain-libs, we now have a solid foundation around which to model our Cardano type in the SDK to better reflect Shelley.

We don't need to model all elements made available through the new lib, but we need to ensure our model better reflects the version of Cardano that the SDK is first targetted to support.

This remodelling is a prerequisite to integrating with the node client the Plutus team are working on.