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/extras/HTMLPurifierExtras.autoload.php

@@ -1,26 +0,0 @@
-<?php
-
-/**
- * @file
- * Convenience file that registers autoload handler for HTML Purifier.
- *
- * @warning
- *      This autoloader does not contain the compatibility code seen in
- *      HTMLPurifier_Bootstrap; the user is expected to make any necessary
- *      changes to use this library.
- */
-
-if (function_exists('spl_autoload_register')) {
-    spl_autoload_register(array('HTMLPurifierExtras', 'autoload'));
-    if (function_exists('__autoload')) {
-        // Be polite and ensure that userland autoload gets retained
-        spl_autoload_register('__autoload');
-    }
-} elseif (!function_exists('__autoload')) {
-    function __autoload($class)
-    {
-        return HTMLPurifierExtras::autoload($class);
-    }
-}
-
-// vim: et sw=4 sts=4