added submenu, made sure submenu visibility is always up to date

public/app/features/dashboard/components/SubMenu/SubMenu.tsx

@@ -0,0 +1,36 @@
+// Libaries
+import React, { PureComponent } from 'react';
+
+// Utils & Services
+import { AngularComponent, getAngularLoader } from 'app/core/services/AngularLoader';
+
+// Types
+import { DashboardModel } from '../../state/DashboardModel';
+
+export interface Props {
+  dashboard: DashboardModel | null;
+}
+
+export class SubMenu extends PureComponent<Props> {
+  element: HTMLElement;
+  angularCmp: AngularComponent;
+
+  componentDidMount() {
+    const loader = getAngularLoader();
+
+    const template = '<dashboard-submenu dashboard="dashboard" />';
+    const scopeProps = { dashboard: this.props.dashboard };
+
+    this.angularCmp = loader.load(this.element, scopeProps, template);
+  }
+
+  componentWillUnmount() {
+    if (this.angularCmp) {
+      this.angularCmp.destroy();
+    }
+  }
+
+  render() {
+    return <div ref={element => this.element = element} />;
+  }
+}

public/app/features/dashboard/components/SubMenu/index.ts

@@ -1 +1,2 @@
 export { SubMenuCtrl } from './SubMenuCtrl';
+export { SubMenu } from './SubMenu';