refs https://github.com/TryGhost/Toolbox/issues/214
- The values configuration for the settings table need to become configurable to be able to run our test environment with a pre-defined set of configurations (e.g Stripe-related values).
- This change makes it possible to define the default settings file location (currently a JSON)
- A new key is now exposed through the "paths.defaultSettings" key in settings, which can be overloaded for the needs of the environment
