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/CommonAttributes.php

@@ -0,0 +1,31 @@
+<?php
+
+class HTMLPurifier_HTMLModule_CommonAttributes extends HTMLPurifier_HTMLModule
+{
+    /**
+     * @type string
+     */
+    public $name = 'CommonAttributes';
+
+    /**
+     * @type array
+     */
+    public $attr_collections = array(
+        'Core' => array(
+            0 => array('Style'),
+            // 'xml:space' => false,
+            'class' => 'Class',
+            'id' => 'ID',
+            'title' => 'CDATA',
+        ),
+        'Lang' => array(),
+        'I18N' => array(
+            0 => array('Lang'), // proprietary, for xml:lang/lang
+        ),
+        'Common' => array(
+            0 => array('Core', 'I18N')
+        )
+    );
+}
+
+// vim: et sw=4 sts=4