Link to a detached Styleguide without a project

[freak4pc]

With the introduction of sectioned projects, there is a very valid use-case of companies that use a project-per-feature and a single base style guide.

In these scenarios, using Prism with a single Project ID is subpar.

We should support using a Styleguide ID, instead of a Project ID, for these specific use-cases.

This would be an if/or scenario, e.g. - you can either use Prism with a Styleguide, or a Project, but not both (which makes sense)