Move 'monitoring.json' schema to sub folder 'data-types/monitoring'
Changing indentation of the 'required' field

- Before it was included as a properties property, but this was wrong
- Now it should be parsed correctly as a required field
Return the schemas folder, rather than writing out the list
Change the description to match the backdrop data-set referencing convention
Merge pull request #157 from alphagov/monitoringcleanup

Monitoring schema cleanup