Expose route name -> path map

[thatmarvin]

We want to do this so that urlFor() can be used outside of the context of the app it's used in.

• Create a middleware to expose /routes.json, which is just an array of { "route name": "path" }
• Enforce a concept of public/private routes. Probably just a private: true flag, and possibly a configurable global default
• Figure out a good way to consume routes.json. Best way is to probably consume and cache the json in app.js on bootstrap. What if we need to support multiple sets of routes, like both www and admin routes?