Replace existing autoloader with Composer-supplied

- Move Friendica namespace to `src`
- Move required `ezyang/htmlpurifier` to vendor
- Remove existing static autoloader
- Change boot.php reference to the autoloader

vendor/ezyang/htmlpurifier/library/HTMLPurifier/AttrTransform/ScriptRequired.php

@@ -0,0 +1,23 @@
+<?php
+
+/**
+ * Implements required attribute stipulation for <script>
+ */
+class HTMLPurifier_AttrTransform_ScriptRequired extends HTMLPurifier_AttrTransform
+{
+    /**
+     * @param array $attr
+     * @param HTMLPurifier_Config $config
+     * @param HTMLPurifier_Context $context
+     * @return array
+     */
+    public function transform($attr, $config, $context)
+    {
+        if (!isset($attr['type'])) {
+            $attr['type'] = 'text/javascript';
+        }
+        return $attr;
+    }
+}
+
+// vim: et sw=4 sts=4