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/DefinitionCache/Null.php

@@ -0,0 +1,39 @@
+<?php
+
+/**
+ * Null cache object to use when no caching is on.
+ */
+class HTMLPurifier_DefinitionCache_Null extends HTMLPurifier_DefinitionCache
+{
+
+    public function add($def, $config) {
+        return false;
+    }
+
+    public function set($def, $config) {
+        return false;
+    }
+
+    public function replace($def, $config) {
+        return false;
+    }
+
+    public function remove($config) {
+        return false;
+    }
+
+    public function get($config) {
+        return false;
+    }
+
+    public function flush($config) {
+        return false;
+    }
+
+    public function cleanup($config) {
+        return false;
+    }
+
+}
+
+// vim: et sw=4 sts=4