Add and configure service worker

[oskarrough]

I've had trouble with service workers before. They make development harder. But they also make the site quite a bit faster and able to render something when offline.

But ember-service-worker recently added a feature to handle caching http://ember-service-worker.com/documentation/configuration/#versioning. So every time we yarn build, a new filename is generated and caching shouldn't be an issue. Let's see?

[4www]

Neetos!

Feedback:

• "no internet" message disappear when dummy app is removed

Feature idea:

• when offline, "file input" to select a folder with the offline tracks (and would work exactly like r4)

[oskarrough]

Right about the offline message. It only happens in production. In development the offline message stays there, meaning the app doesn't render. Don't know why.

Can test with ember serve -prod. Gotta find a solution for that before merging.

[4www]

It's perfect, let's go with that and make it a component when ready for some offline support.