Destructure underscore lib imports in front-end.

app/panel/components/BuildingBlocks/DonutGraph.jsx

@@ -11,7 +11,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0
  */
 
-import _ from 'underscore';
+import { throttle } from 'underscore';
 import React from 'react';
 import ClassNames from 'classnames';
 import {
@@ -178,7 +178,7 @@ class DonutGraph extends React.Component {
 	 * @param  {Array} categories list of categories detected on the site
 	 * @param  {Object} options    options for the graph
 	 */
-	bakeDonut = _.throttle(this._bakeDonut.bind(this), 600, { leading: true, trailing: true }) // matches panelData#updatePanelUI throttling
+	bakeDonut = throttle(this._bakeDonut.bind(this), 600, { leading: true, trailing: true }) // matches panelData#updatePanelUI throttling
 
 	_bakeDonut(categories, options) {
 		const {

app/panel/components/BuildingBlocks/StatsGraph.jsx

@@ -11,7 +11,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0
  */
 
-import _ from 'underscore';
+import { isEqual } from 'underscore';
 import React from 'react';
 import * as D3 from 'd3';
 
@@ -30,7 +30,7 @@ class StatsGraph extends React.Component {
 	 * Lifecycle event
 	 */
 	componentDidUpdate(prevProps) {
-		if (!_.isEqual(prevProps, this.props)) {
+		if (!isEqual(prevProps, this.props)) {
 			this.generateGraph();
 		}
 	}