Make Marlowe Chain-Agnostic

[bwbush]

This discussion regards removing Cardano-specific dependencies from the Marlowe specification and its Haskell implementation.

Background information:

• Pull request Make Marlowe chain agnostic marlowe-cardano#182, which proposes changes to Marlowe's Haskell implementation to make it blockchain agnostic
• https://github.com/input-output-hk/marlowe, which contains Marlowe specification, semantics, Isabelle, and reference Haskell