Get Started: Server Rendering

This PR adds the necessary HTML/CSS/server-side plumbing to get server-rendering working the `/start/` route. All params can be rendered on the server.

Here are some examples of routes that work:

```
http://127.0.0.1:5000/start/
http://127.0.0.1:5000/start/?med=screen and (min-width:48em)
http://127.0.0.1:5000/start/?med=36em&lrg=60em&cols=4&fonts=sans-serif;
```