enable save button only if dashboard is dirty

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

@@ -18,6 +18,8 @@ export class DashboardComponent implements OnInit {
 
   dashboard?: Dashboard = undefined;
 
+  pristineDashboardJSON?: string = undefined;
+
   error = "";
 
   plotWidgetRenderData: PlotWidgetRenderData[] = [];
@@ -34,6 +36,7 @@ export class DashboardComponent implements OnInit {
       this.service.getDashboard(<string>this.route.snapshot.paramMap.get("id")).subscribe({
         'next':(dashboard: Dashboard) => {
           this.dashboard = dashboard;
+          this.pristineDashboardJSON = JSON.stringify(dashboard);
           this.repairArrangement();
 
           dashboard.plots.forEach(p => {
@@ -54,6 +57,10 @@ export class DashboardComponent implements OnInit {
       });
   }
 
+  isDirty() {
+    return this.pristineDashboardJSON !== JSON.stringify(this.dashboard);
+  }
+
   loadImages(index: number, plotWidgetQueue: PlotWidgetRenderData[]) {
 
     if (index < plotWidgetQueue.length){
@@ -161,6 +168,7 @@ export class DashboardComponent implements OnInit {
           duration: 5000,
           verticalPosition: 'top'
         });
+        this.pristineDashboardJSON = JSON.stringify(this.dashboard);
       }
     });
   }