Add eslint:recommended and update rules and globals

src/components/htmlvideoplayer/plugin.js

@@ -357,6 +357,7 @@ define(['browser', 'require', 'events', 'apphost', 'loading', 'dom', 'playbackMa
             return new Promise(function (resolve, reject) {
 
                 require(['shaka'], function () {
+                    /* globals shaka */
 
                     var player = new shaka.Player(elem);
 

src/components/polyfills/focusPreventScroll.js

@@ -12,6 +12,7 @@ if (HTMLElement.prototype.nativeFocus === undefined) {
             }, true);
 
             var opts = Object.defineProperty({}, "preventScroll", {
+                // eslint-disable-next-line getter-return
                 get: function () {
                     supportsPreventScrollOption = true;
                 }

src/components/polyfills/objectassign.js

@@ -11,6 +11,7 @@ if (typeof Object.assign != 'function') {
                 var source = arguments[index];
                 if (source !== undefined && source !== null) {
                     for (var nextKey in source) {
+                        // eslint-disable-next-line no-prototype-builtins
                         if (source.hasOwnProperty(nextKey)) {
                             output[nextKey] = source[nextKey];
                         }

src/components/serviceworker/notifications.js

@@ -1,3 +1,4 @@
+/* eslint-env serviceworker */
 (function () {
     'use strict';
 

src/components/skinManager.js

@@ -162,6 +162,7 @@ define(['apphost', 'userSettings', 'browser', 'events', 'pluginManager', 'backdr
     function playSound(path, volume) {
         lastSound = new Date().getTime();
         require(['howler'], function (howler) {
+            /* globals Howl */
             try {
                 var sound = new Howl({
                     src: [path],

src/components/youtubeplayer/plugin.js

@@ -1,5 +1,6 @@
 define(['require', 'events', 'browser', 'appRouter', 'loading'], function (require, events, browser, appRouter, loading) {
     "use strict";
+    /* globals YT */
 
     function zoomIn(elem, iterations) {
         var keyframes = [