Add static HtmlUtils/StringUtils into edx namespace

This is a temporary workaround for code that needs
access to these classes from the UI Toolkit but
without using RequireJS.

common/static/common/js/common_libraries.js

@@ -1 +1,21 @@
-define(['domReady!', 'jquery', 'backbone', 'underscore', 'gettext']);
+define([
+        'edx-ui-toolkit/js/utils/string-utils',
+        'edx-ui-toolkit/js/utils/html-utils',
+        'domReady!',
+        'jquery',
+        'backbone',
+        'underscore',
+        'gettext'
+    ],
+    function(StringUtils, HtmlUtils) {
+        'use strict';
+
+        // Install utility classes in the edX namespace to make them
+        // available to code that doesn't use RequireJS,
+        // e.g. XModules and XBlocks.
+        if (window) {
+            window.edx = window.edx || {};
+            window.edx.StringUtils = StringUtils;
+            window.edx.HtmlUtils = HtmlUtils;
+        }
+    });