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/components/App/index.tsx

@@ -36,12 +36,17 @@ export default class App extends Component<Props, State> {
   constructor() {
     super();
 
-    import('../compress').then((module) => {
+    import(
+      /* webpackChunkName: "main-app" */
+      '../compress',
+    ).then((module) => {
       this.setState({ Compress: module.default });
     }).catch(() => {
       this.showSnack('Failed to load app');
     });
 
+    navigator.serviceWorker.register('../../sw');
+
     // In development, persist application state across hot reloads:
     if (process.env.NODE_ENV === 'development') {
       this.setState(window.STATE);