Add publish and subcribe to ScanCode scan

[pombredanne]

As a practical application of FederatedCode, I would like to have an application such that we can publish a ScanCode scan for a Package to the FederatedCode backing git repo(s)/server(s) and advertise it over FederatedCode pub/sub. Then I should be able to discover this scan querying the ActivityPub server and fetch it from the backing git repo on the receiving end.

This could include:

• Create script to store and publish a ScanCode scan in the FederatedCode Git-based architecture
• Advertise a pushed ScanCode scan in the FederatedCode ActivityPub server
• Create script to discover the scan for a package in the FederatedCode ActivityPub server and to fetch it from the backing git repo(s)