Use serviceworker to cache github responses

[SleeplessByte]

• Cache app
• Cache github content
• Ensure it releases the cache on a "hard reload" (Cache-control: no-cache)
• Show a snackbar on new version available, and reload after a delay
• CACHE_FIRST but still load network and replace. Emit custom event if necessary to reload data on the page. Use a hook, so we don't need to keep track manually.

I recommend workerbox.