Added PWA support (#40)

public/sw.js

@@ -0,0 +1,22 @@
+self.addEventListener('push', function (event) {
+  if (event.data) {
+    const data = event.data.json()
+    const options = {
+      body: data.body,
+      icon: data.icon || '/icon.png',
+      badge: '/badge.png',
+      vibrate: [100, 50, 100],
+      data: {
+        dateOfArrival: Date.now(),
+        primaryKey: '2',
+      },
+    }
+    event.waitUntil(self.registration.showNotification(data.title, options))
+  }
+})
+
+self.addEventListener('notificationclick', function (event) {
+  console.log('Notification click received.')
+  event.notification.close()
+  event.waitUntil(clients.openWindow('/'))
+})