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/AttrDef/HTML/FrameTarget.php

@@ -0,0 +1,38 @@
+<?php
+
+/**
+ * Special-case enum attribute definition that lazy loads allowed frame targets
+ */
+class HTMLPurifier_AttrDef_HTML_FrameTarget extends HTMLPurifier_AttrDef_Enum
+{
+
+    /**
+     * @type array
+     */
+    public $valid_values = false; // uninitialized value
+
+    /**
+     * @type bool
+     */
+    protected $case_sensitive = false;
+
+    public function __construct()
+    {
+    }
+
+    /**
+     * @param string $string
+     * @param HTMLPurifier_Config $config
+     * @param HTMLPurifier_Context $context
+     * @return bool|string
+     */
+    public function validate($string, $config, $context)
+    {
+        if ($this->valid_values === false) {
+            $this->valid_values = $config->get('Attr.AllowedFrameTargets');
+        }
+        return parent::validate($string, $config, $context);
+    }
+}
+
+// vim: et sw=4 sts=4