Service Worker integration

First, thanks for the project, it's really cool!

So, I was thinking that will be really nice to support Service Worker to improve a the user experience, initial rendering time... even maybe support an **offline mode** (not sure if makes sense).

Since you are using Broccoli, maybe this will be "easy" to integrate? https://github.com/jkleinsc/broccoli-serviceworker

Just a suggestion, great work! ^^