Create a RegisterableEdition class

This is an edition which can be registered with Panopticon using the 
Registerer class.
Register artefacts with Panopticon on publish

Create a new service listener which will register a detailed guide with 
Panopticon when it is published or force published.
Include industry sector tags in a RegisterableEdition
Refactor Panopticon registration rake task

The logic to build up an artefact from a detailed guide is now 
encapsulated in the RegisterableEdition class, so we can make this code 
simpler.
Make clearer assertions on RegisterableEdition unit tests
Set the state for a RegisterableEdition based on the edition
Merge pull request #1235 from alphagov/panopticon-as-a-service

Register a detailed guide with Panopticon on publish