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.func.php

@@ -1,25 +0,0 @@
-<?php
-
-/**
- * @file
- * Defines a function wrapper for HTML Purifier for quick use.
- * @note ''HTMLPurifier()'' is NOT the same as ''new HTMLPurifier()''
- */
-
-/**
- * Purify HTML.
- * @param string $html String HTML to purify
- * @param mixed $config Configuration to use, can be any value accepted by
- *        HTMLPurifier_Config::create()
- * @return string
- */
-function HTMLPurifier($html, $config = null)
-{
-    static $purifier = false;
-    if (!$purifier) {
-        $purifier = new HTMLPurifier();
-    }
-    return $purifier->purify($html, $config);
-}
-
-// vim: et sw=4 sts=4