Get a better handle on how Service Worker stuff needs to be structured

[thisisaaronland]

Specifically so that updates to the Fingerprint application can be propagated without having to resort to purging all the cached data for an entire domain.

See also:

• https://developer.mozilla.org/en-US/docs/Web/API/Service_Worker_API/Using_Service_Workers
• https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorkerGlobalScope/install_event
• https://developer.mozilla.org/en-US/docs/Web/API/Cache
• https://stackoverflow.com/questions/41636754/how-to-clear-a-service-worker-cache-in-firefox