added id tag to Panels for html bookmarking on longer Dashboards

public/app/features/dashboard/dashgrid/DashboardGrid.tsx

@@ -177,7 +177,7 @@ export class DashboardGrid extends React.Component<DashboardGridProps, any> {
     for (let panel of this.dashboard.panels) {
       const panelClasses = classNames({ panel: true, 'panel--fullscreen': panel.fullscreen });
       panelElements.push(
-        <div key={panel.id.toString()} className={panelClasses}>
+        <div key={panel.id.toString()} className={panelClasses} id={`panel-${panel.id.toString()}`}>
           <DashboardPanel panel={panel} getPanelContainer={this.props.getPanelContainer} />
         </div>
       );