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/HTMLModule/NonXMLCommonAttributes.php

@@ -0,0 +1,20 @@
+<?php
+
+class HTMLPurifier_HTMLModule_NonXMLCommonAttributes extends HTMLPurifier_HTMLModule
+{
+    /**
+     * @type string
+     */
+    public $name = 'NonXMLCommonAttributes';
+
+    /**
+     * @type array
+     */
+    public $attr_collections = array(
+        'Lang' => array(
+            'lang' => 'LanguageCode',
+        )
+    );
+}
+
+// vim: et sw=4 sts=4