use port 17333 by default

Not sure how this is supposed to work. To be able to support
Angular's development server and Spring as a standalone application
I had to hardcode the port Spring uses.
The problem is, that Angular runs on port 4200. Angular is compiled
to static files. So I cannot dynamically add the port that is
configured for Spring. But Angular has to be able to talk to the
Spring application.
I chose port 17333, because it does not collide with the standard
Tomcat port (8080).

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

@@ -133,7 +133,7 @@ export class VisualizationPageComponent implements OnInit {
     
     this.plotService.sendPlotRequest(request).subscribe(function(plotResponse){
       console.log("response: " + JSON.stringify(plotResponse));
-      that.plotView.imageUrl = "http://"+window.location.hostname+':8080/'+plotResponse.imageUrl;
+      that.plotView.imageUrl = "http://"+window.location.hostname+':17333/'+plotResponse.imageUrl;
       document.dispatchEvent(new Event("invadersPause", {}));
     },
     error => {