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

library/ezyang/htmlpurifier/library/HTMLPurifier/HTMLModule/Nofollow.php

@@ -1,25 +0,0 @@
-<?php
-
-/**
- * Module adds the nofollow attribute transformation to a tags.  It
- * is enabled by HTML.Nofollow
- */
-class HTMLPurifier_HTMLModule_Nofollow extends HTMLPurifier_HTMLModule
-{
-
-    /**
-     * @type string
-     */
-    public $name = 'Nofollow';
-
-    /**
-     * @param HTMLPurifier_Config $config
-     */
-    public function setup($config)
-    {
-        $a = $this->addBlankElement('a');
-        $a->attr_transform_post[] = new HTMLPurifier_AttrTransform_Nofollow();
-    }
-}
-
-// vim: et sw=4 sts=4