Intro tutorial

Adding `tutorial` as a query parameter to the designer url will launch a brief walkthrough. The walkthrough HTML content is defined in `public/tutorial/intro.html` and the walkthrough itself is defined in `public/tutorial/intro.js`. 

The content is not yet complete or accurate, but the basic mechanism is ready for a first review. 
Since you're adding these right into the dom, can you namespace them? Or maybe use a `data-` attribute instead of `id`?