Consistency & documentation of which URLs are used #246

We should document and stick to some pattern for what URLs are used, in both the development server and a production deploy.

The rationale is, if you are setting up a proxy, you might want to route a certain path to a different server. You need to choose a path that isn't used by this React app, which means you have to know what paths are used. If you route /files/* to a different port, and later we switch the build script so that it generates files prefixed with /files/, your setup will break.

My suggestion is, in production only use the URL patterns / and /static/*. In the dev server, use those two but also /dev/* for non-static content - ie the websocket. Then any routing layer only has a few things to worry about.