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/URIScheme/http.php

@@ -0,0 +1,36 @@
+<?php
+
+/**
+ * Validates http (HyperText Transfer Protocol) as defined by RFC 2616
+ */
+class HTMLPurifier_URIScheme_http extends HTMLPurifier_URIScheme
+{
+    /**
+     * @type int
+     */
+    public $default_port = 80;
+
+    /**
+     * @type bool
+     */
+    public $browsable = true;
+
+    /**
+     * @type bool
+     */
+    public $hierarchical = true;
+
+    /**
+     * @param HTMLPurifier_URI $uri
+     * @param HTMLPurifier_Config $config
+     * @param HTMLPurifier_Context $context
+     * @return bool
+     */
+    public function doValidate(&$uri, $config, $context)
+    {
+        $uri->userinfo = null;
+        return true;
+    }
+}
+
+// vim: et sw=4 sts=4