Move no realistic dashboard into experimental directory

We have to manually blacklist NRD from all the automated tools we use for dashboards.
Moving it into `experimental` allows it to be automatically ignored from any lists we create, and probably is a more sensible place to keep it generally since it's only used for development.
Add script to generate services list from dashboards configs
Remove services.json from version control

It's generated automatically now, so doesn't need to be in git.
Generate services.json as part of app startup
Check dashboard stubs based on page-type

Instead of maintaining a regex of blacklisted files, just assume anything that isn't a dashboard isn't a dashboard.
Tidied up file path declaration
Merge pull request #419 from alphagov/feature/services-json-generator

Feature/services json generator