Get rid of requirement for /STAGE base path

Unfortunately with the way AWS API Gateway currently works, requests to say `/style.css` won't even make it to your app (or Up). The `/development` (and other stage) prefixes are a requirement at the moment, it's just a really annoying choice that AWS made, so it must be `/development/style.css` or `./style.css` (relative).

If you use custom domains this won't be a problem. The vanity urls (#179) would also help mitigate this. I'm hoping AWS will mention some new stuff at Reinvent.