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/ChildDef/Optional.php

@@ -1,45 +0,0 @@
-<?php
-
-/**
- * Definition that allows a set of elements, and allows no children.
- * @note This is a hack to reuse code from HTMLPurifier_ChildDef_Required,
- *       really, one shouldn't inherit from the other.  Only altered behavior
- *       is to overload a returned false with an array.  Thus, it will never
- *       return false.
- */
-class HTMLPurifier_ChildDef_Optional extends HTMLPurifier_ChildDef_Required
-{
-    /**
-     * @type bool
-     */
-    public $allow_empty = true;
-
-    /**
-     * @type string
-     */
-    public $type = 'optional';
-
-    /**
-     * @param array $children
-     * @param HTMLPurifier_Config $config
-     * @param HTMLPurifier_Context $context
-     * @return array
-     */
-    public function validateChildren($children, $config, $context)
-    {
-        $result = parent::validateChildren($children, $config, $context);
-        // we assume that $children is not modified
-        if ($result === false) {
-            if (empty($children)) {
-                return true;
-            } elseif ($this->whitespace) {
-                return $children;
-            } else {
-                return array();
-            }
-        }
-        return $result;
-    }
-}
-
-// vim: et sw=4 sts=4