WIP: Fix service worker

[marcoow]

This is a WIP for fixing the service worker by:

• enabling asset fingerprinting (basically as part of upgrading to the latest blueprint)
• enabling the service worker again
• updating the cache for successful doc requests so we're serving the latest version from the service worker when the user is offline

The only problem I see is that eagerly caching the assets doesn't work because we're not replacing the asset names in workers/service.ts as part of the build process (yet) and I'm not sure what the best way to do that is. So currently the service worker would cache e.g. app.js on installation but the browser will ask for app-hash.js later.

closes #28