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. 
You probably don't need `var Tutorial`. `function Tutorial` should plop `Tutorial` into this scope to grab and return below.