Add PWA offline support for standalone web app install

[stevenpovlitz]

Addresses #182

This is my first PR to meshtastic and meshtastic/web, please point out contribution policies and conventions. The code is pulled from the default service worker setup from running:

npx create-react-app my-app --template cra-template-pwa-typescript

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[dzienisz]

I like this idea of making this app installable.

[danditomaso]

This PR looks like its missing workbox-core being added to the package.json. As well it looks like it uses functions from workbox-core v3 instead of using the latest v4 version, functions such as clientsClaim doesn't exist in v4.

[KomelT]

Closing this PR because this work was already merged in #468