Add sample panopticon API credentials for development

Without the constant in existence the panopticon rake task can't be run
in development mode/on the development VM (panopticon returns 401
Unauthorized because no bearer token is provided at all).

With the token in existence, no matter its content, panopticon operates
correctly in development.
Merge pull request #51 from alphagov/add-sample-panopticon-credentials

Add sample panopticon API credentials for development