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/AttrTransform/SafeEmbed.php

@@ -0,0 +1,25 @@
+<?php
+
+class HTMLPurifier_AttrTransform_SafeEmbed extends HTMLPurifier_AttrTransform
+{
+    /**
+     * @type string
+     */
+    public $name = "SafeEmbed";
+
+    /**
+     * @param array $attr
+     * @param HTMLPurifier_Config $config
+     * @param HTMLPurifier_Context $context
+     * @return array
+     */
+    public function transform($attr, $config, $context)
+    {
+        $attr['allowscriptaccess'] = 'never';
+        $attr['allownetworking'] = 'internal';
+        $attr['type'] = 'application/x-shockwave-flash';
+        return $attr;
+    }
+}
+
+// vim: et sw=4 sts=4