Consistency & documentation of which URLs are used

[lacker]

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.

[gaearon]

cc @ForbesLindesay who also wanted this

[gaearon]

#278 gives us /static

[gaearon]

We consistently use /static for any assets, and we serve index.html or proxy fallback for any other URL depending on whether you have proxy and whether accept header contains text/html. Seems pretty consistent to me.