Add website to client repository

Closes #1567

The main reason I'm not simply merging Annika's PR is because this
way makes it clearer that I'm taking responsibility for all this
code, that it's mostly code I wrote, and also because it makes it
easier to ensure that none of the files have been changed.

(Not that I don't personally trust Annika, but I have something
resembling an obligation to users not to expose them to risks based
on personal trust.)

website/lib/htmlpurifier/HTMLPurifier/AttrTransform/ScriptRequired.php

@@ -0,0 +1,16 @@
+<?php
+
+/**
+ * Implements required attribute stipulation for <script>
+ */
+class HTMLPurifier_AttrTransform_ScriptRequired extends HTMLPurifier_AttrTransform
+{
+    public function transform($attr, $config, $context) {
+        if (!isset($attr['type'])) {
+            $attr['type'] = 'text/javascript';
+        }
+        return $attr;
+    }
+}
+
+// vim: et sw=4 sts=4