Support route chunking

Is it in your plans to support chunks for individual routes? For example, when you land on `/`, you only load what you need for `/`.

I took your repo and added this in for my own project so if you'd like me to help make a PR for this I'm happy to do that. I'm not 100% sure that my implementation is the best or most efficient as I tried to copy the implementation from other projects and my own research, so I would be happy for you to help review and improve it. And of course, I'm not as familiar as you are with the internals of this project, especially the server-side rendering.

In short, I changed all of the routes to use `getComponent` to allow webpack to create a chunk for each route, that's only loaded when you visit that route. I also had to change the way the client/server renders the app.

_Also, I'm not sure on how you like PRs to be structured for this repo, since you have several trees for each progressive feature._