Modularize code

Split JS into per-class files
Cut parts of trweb class out
Move init code from event handler to constructor

js/trdom_menubar.js

@@ -0,0 +1,19 @@
+"use strict";
+
+class trdom_menubar {
+    #element = document.createElement('div');
+    getElement() {
+        return this.#element;
+    }
+
+    #menuNodes = {};
+    addMenuNode(name, element, after = null) {
+        //TODO: add ID checks and after support
+        this.#menuNodes[name] = element;
+        this.#element.appendChild(element);
+    }
+
+    constructor () {
+        this.#element.classList.add('trweb_header');
+    }
+}