improve error messages

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

@@ -1,3 +1,4 @@
+import { HttpErrorResponse } from '@angular/common/http';
 import { Component, OnInit } from '@angular/core';
 import { MatDialog } from '@angular/material/dialog';
 import { Dashboard, DashboardCreationData, DashboardList, DashboardService } from '../dashboard.service';
@@ -31,8 +32,12 @@ export class DashboardPageComponent implements OnInit {
         this.dataSource = dashboardList.dashboards;
         this.loading = false;
       },
-      'error': () => {
-        this.error = "Failed to load dashboards.";
+      'error': (error: HttpErrorResponse) => {
+        if (error.status == 504){
+          this.error = "Server Unreachable";
+        }else{
+          this.error = "Failed to load dashboards";
+        }
         this.loading = false;
       }
     });