use the invaders game as 'loading screen'

pdb-js/src/app/visualization-page/visualization-page.component.ts

@@ -107,16 +107,19 @@ export class VisualizationPageComponent implements OnInit {
     
     that.plotView.imageUrl = '';
     that.galleryView.show=false;
+    document.dispatchEvent(new Event("invadersStart", {}));
     
     const request = this.createPlotRequest();
     
     this.plotService.sendPlotRequest(request).subscribe(function(plotResponse){
       console.log("response: " + JSON.stringify(plotResponse));
       that.plotView.imageUrl = "http://"+window.location.hostname+':8080/'+plotResponse.imageUrl;
+      document.dispatchEvent(new Event("invadersPause", {}));
     },
     error => {
       that.plotView.imageUrl = '';
       that.showError(error.error.message);
+      document.dispatchEvent(new Event("invadersPause", {}));
     });
   }