update new version experience

This changes the new version message to be more user-friendly and allows
using the new version without restarting the browser or clearing the
cache.

src/components/notification-i18n.en.json

@@ -13,6 +13,9 @@
         "error": "{errorMessage}"
     },
     "serviceWorker": {
-        "update": "New content is available and will be used when all tabs for this page are closed.'"
+        "update": {
+            "message": "A new version of {appName} is available. Click {action} to start using the new version.",
+            "action": "Restart"
+        }
     }
 }

src/components/notification-i18n.ts

@@ -9,7 +9,8 @@ export enum MessageId {
     BleGattServiceNotFound = 'ble.gattServiceNotFound',
     BleNoWebBluetooth = 'ble.noWebBluetooth',
     ProgramChanged = 'editor.programChanged',
-    ServiceWorkerUpdate = 'serviceWorker.update',
+    ServiceWorkerUpdateMessage = 'serviceWorker.update.message',
+    ServiceWorkerUpdateAction = 'serviceWorker.update.action',
     YesReloadProgram = 'editor.yesReloadProgram',
     MpyError = 'mpy.error',
 }