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/Text.php

@@ -0,0 +1,21 @@
+<?php
+
+/**
+ * Validates arbitrary text according to the HTML spec.
+ */
+class HTMLPurifier_AttrDef_Text extends HTMLPurifier_AttrDef
+{
+
+    /**
+     * @param string $string
+     * @param HTMLPurifier_Config $config
+     * @param HTMLPurifier_Context $context
+     * @return bool|string
+     */
+    public function validate($string, $config, $context)
+    {
+        return $this->parseCDATA($string);
+    }
+}
+
+// vim: et sw=4 sts=4