Refactor Blockchain Code

[zupzup]

• Restructure Blockchain code so that it can be used from the service structure
  • Put behind a trait for testability
  • The blockchain code should be self-contained and not rely on fetching bills/keys/anything from the file system - these values should always be passed in from outside.
  • Blockchain code should be passed data, make changes to it, then return the new state, which can then be persisted by the caller
• Add error-handling and propagate through code-base
• Make it testable
• Write tests
• Document it