blockchain observer daemon - sample implementation

[monkeypants]

There are many reasons why someone would want to "observe" notary activities:

• audit the performance of a notary (or all notaries) - are they publishing what they promise to publish?
• loose-coupled replication of notarisation data
• use of blockchain notary to coordinate decentralised/distributed processes

It would be great if we had an open source reference implementation of a daemon that does this. Even better if it used a plugin architecture to simplify development of applications that require blockchain observer.

Initial implementation could probably use 3rd party blockchain service and IPFSD, but ideally that should also be configurable:

• local/controlled IPFSD, so that the daemon can pin files to achieve reliable replication of HOC data (avoid garbage collection)
• local blockchain node, to participate in consensus and avoid dependency on 3rd party services.