add range selection in plot view

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

@@ -85,6 +85,11 @@ export class VisualizationPageComponent implements OnInit {
     
   plot(){
     const that = this;
+    
+    that.plotView.errorMessage = '';
+    that.plotView.imageUrl = '';
+    
+    
     var aggregates = [];
     aggregates.push(this.selectedPlotType.value.id);
     if (this.selectedCombinePlotType.value){
@@ -111,6 +116,7 @@ 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.errorMessage = '';
     },
     error => {
       that.plotView.imageUrl = '';