Adds a javascript widget tutorial to the dev tiddlywiki edition (#7016)

* Initial widget tutorials extracted from https://btheado.github.io/tw-widget-tutorial/

* Fixes for refresh behavior change

editions/dev/tiddlers/javascript-widget-tutorial/hello.js

@@ -0,0 +1,35 @@
+/*\
+
+Hello, World widget
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+var Widget = require("$:/core/modules/widgets/widget.js").widget;
+
+var MyWidget = function(parseTreeNode,options) {
+	this.initialise(parseTreeNode,options);
+};
+
+/*
+Inherit from the base widget class
+*/
+MyWidget.prototype = new Widget();
+
+/*
+Render this widget into the DOM
+*/
+MyWidget.prototype.render = function(parent,nextSibling) {
+	this.parentDomNode = parent;
+	var textNode = this.document.createTextNode("Hello, World!");
+	parent.insertBefore(textNode,nextSibling);
+	this.domNodes.push(textNode);
+};
+
+exports.hello = MyWidget;
+
+})();