Add a serviceworker (#234)

* Add a serviceworker

* rename + fix random extra character

* Fixing worker typings

* Fixing types properly this time.

* Once of those rare cases where this matters.

* Naming the things.

* Move registration to the app (so we can use snackbar later)

* Moving SW plugin later so it picks up things like HTML

* MVP service worker

* Two stage-service worker

* Fix prerendering by conditionally awaiting Custom Elements polyfill.

* Fix icon 404's

* add doc comment to autoswplugin

* Fix type

src/index.ts

@@ -1,9 +1,14 @@
 declare module '@webcomponents/custom-elements';
 
-(async function () {
-  if (!('customElements' in self)) {
-    await import('@webcomponents/custom-elements');
-  }
-
+function init() {
   require('./init-app.tsx');
-})();
+}
+
+if (!('customElements' in self)) {
+  import(
+    /* webpackChunkName: "wc-polyfill" */
+    '@webcomponents/custom-elements',
+  ).then(init);
+} else {
+  init();
+}