Real-time communication with frontend

- Frontend shows heatmap of most visit places
- Maximum accuracy can now be set
- Fix bug where battery chart filtered values wrongly

frontend/src/app/app.module.ts

@@ -14,6 +14,7 @@ import { LoginComponent } from './login/login.component';
 import { MapComponent } from './map/map.component';
 import { UserComponent } from './user/user.component';
 import { DashboardWidgetComponent } from './dashboard-widget/dashboard-widget.component';
+import { IMqttServiceOptions, MqttModule } from 'ngx-mqtt';
 
 @NgModule({
   declarations: [
@@ -31,6 +32,7 @@ import { DashboardWidgetComponent } from './dashboard-widget/dashboard-widget.co
     BrowserAnimationsModule,
     FormsModule,
     HttpClientModule,
+    MqttModule.forRoot({}),
     NgxMapboxGLModule.withConfig({
       accessToken: 'pk.eyJ1IjoibW9uZGVpMSIsImEiOiJja2dsY2ZtaG0xZ2o5MnR0ZWs0Mm82OTBpIn0.NzDWN3P6jJLmci_v3MM1tA'
     }),