Add API for T3 flow and related Bj calls & mocks

* Add JSON API for T3 flow with calls to Bj default mocked.
* Update API validations with base58check and new length checks.
* Update DB schema and contract event persistent state handling.
* Update API error codes/messages.
* Add example debug flow to README for use with website/client
  integration.
Merge branch 'gustav/contracts12'

* gustav/contracts12:
  Add API for T3 flow and related Bj calls & mocks