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/AttrDef/URI/Email.php

@@ -1,20 +0,0 @@
-<?php
-
-abstract class HTMLPurifier_AttrDef_URI_Email extends HTMLPurifier_AttrDef
-{
-
-    /**
-     * Unpacks a mailbox into its display-name and address
-     * @param string $string
-     * @return mixed
-     */
-    public function unpack($string)
-    {
-        // needs to be implemented
-    }
-
-}
-
-// sub-implementations
-
-// vim: et sw=4 sts=4