Add a simple service worker to make an installable app

modules/restserver/src/main/templates/index.html

@@ -46,6 +46,13 @@
          };
         </script>
         <script type="application/javascript" src="{{appExtraJs}}"></script>
+        <script>
+         if('serviceWorker' in navigator) {
+             navigator.serviceWorker
+                 .register('/sw.js')
+                 .then(function() { console.log("Service Worker Registered"); });
+         }
+        </script>
     </body>
 
 </html>