Remove event listeners from (shadow) root instead of window,

make context menus work in Shadow DOM.

Fixes https://github.com/josdejong/jsoneditor/issues/447

src/js/ContextMenu.js

@@ -2,6 +2,14 @@
 
 var util = require('./util');
 
+/**
+ * Node.getRootNode shim
+ * @param  {Node} node node to check
+ * @return {Node}      node's rootNode or `window` if there is ShadowDOM is not supported.
+ */
+function getRootNode(node){
+    return node.getRootNode && node.getRootNode() || window;
+}
 /**
  * A context menu
  * @param {Object[]} items    Array containing the menu structure
@@ -240,7 +248,7 @@ ContextMenu.prototype.show = function (anchor, contentWindow) {
   // create and attach event listeners
   var me = this;
   var list = this.dom.list;
-  var rootNode = list.getRootNode && list.getRootNode() || window;
+  var rootNode = getRootNode(list);
   this.eventListeners.mousedown = util.addEventListener(rootNode, 'mousedown', function (event) {
     // hide menu on click outside of the menu
     var target = event.target;
@@ -281,11 +289,12 @@ ContextMenu.prototype.hide = function () {
 
   // remove all event listeners
   // all event listeners are supposed to be attached to document.
+  var rootNode = getRootNode(this.dom.list);
   for (var name in this.eventListeners) {
     if (this.eventListeners.hasOwnProperty(name)) {
       var fn = this.eventListeners[name];
       if (fn) {
-        util.removeEventListener(window, name, fn);
+        util.removeEventListener(rootNode, name, fn);
       }
       delete this.eventListeners[name];
     }