[REQUEST] Check for updates and reset cache.

[bengarrett]

Whenever the cached, local service worker, or cache is out of date, bring up a banner to prompt for a refresh.

See 1., 2.

caches.keys().then(cacheNames => {
  cacheNames.forEach(cacheName => {
    caches.delete(cacheName);
  });
});

Or workbox-expiration.CacheExpiration, example

Also BroadcastCacheUpdate, example.

[bengarrett]

Added a Update DOSee and the service worker button on the index.html running example.