add pwa support

Frontend/src/app/app.module.ts

@@ -1,4 +1,4 @@
-import { NgModule } from '@angular/core';
+import { NgModule, isDevMode } from '@angular/core';
 import { BrowserModule } from '@angular/platform-browser';
 
 import { AppRoutingModule } from './app-routing.module';
@@ -8,6 +8,7 @@ import { MainViewComponent } from './main-view/main-view.component';
 import { MaterialModule } from './material.module';
 import { LoginPageComponent } from './components/login-page/login-page.component';
 import { HttpClientModule } from '@angular/common/http';
+import { ServiceWorkerModule } from '@angular/service-worker';
 
 
 @NgModule({
@@ -21,7 +22,13 @@ import { HttpClientModule } from '@angular/common/http';
     AppRoutingModule,
     BrowserAnimationsModule,
     MaterialModule,
-    HttpClientModule
+    HttpClientModule,
+    ServiceWorkerModule.register('ngsw-worker.js', {
+      enabled: !isDevMode(),
+      // Register the ServiceWorker as soon as the application is stable
+      // or after 30 seconds (whichever comes first).
+      registrationStrategy: 'registerWhenStable:30000'
+    })
   ],
   providers: [],
   bootstrap: [AppComponent]