Service worker

[trys]

I've modified a Service Worker I've used before on static sites. It's network-first, cache-fallback so it'll work offline, but still get instant content updates without breaking Netlify's cache invalidation. Given all assets are inlined at this stage, this method works well. The main downside is that shaky network conditions will still affect this site, but as it's only html for now, it's not a big deal.

There's a new offline page that lists the key pages. I've also added a trailing slash to the footer links. Netlify auto-redirects /code-of-conduct to /code-of-conduct/ so that would count as separate URLs in the service worker. Plus skipping the redirect will improve performance.

Future ideas for the SW could include:

• Dedicated image cache
• Cache trimming
• Form submit prevention
• Cache-first strategy for non-html assets

[trys]

Not getting 100% PWA lighthouse scores, but that may be related to this issue: GoogleChrome/lighthouse#4541

The start_url is present, but it's claiming it's unusable. I'm beginning to think this is a manifest.json issue, though it's unclear at this point.

[alexcarpenter]

@trys 👏🏻👏🏻👏🏻