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/HTMLModule/SafeScripting.php

@@ -0,0 +1,37 @@
+<?php
+
+/**
+ * A "safe" script module. No inline JS is allowed, and pointed to JS
+ * files must match whitelist.
+ */
+class HTMLPurifier_HTMLModule_SafeScripting extends HTMLPurifier_HTMLModule
+{
+
+    public $name = 'SafeScripting';
+
+    public function setup($config) {
+
+        // These definitions are not intrinsically safe: the attribute transforms
+        // are a vital part of ensuring safety.
+
+        $allowed = $config->get('HTML.SafeScripting');
+        $script = $this->addElement(
+            'script',
+            'Inline',
+            'Empty',
+            null,
+            array(
+                // While technically not required by the spec, we're forcing
+                // it to this value.
+                'type' => 'Enum#text/javascript',
+                'src*'  => new HTMLPurifier_AttrDef_Enum(array_keys($allowed))
+            )
+        );
+        $script->attr_transform_pre[] =
+        $script->attr_transform_post[] = new HTMLPurifier_AttrTransform_ScriptRequired();
+
+    }
+
+}
+
+// vim: et sw=4 sts=4