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

vendor/ezyang/htmlpurifier/library/HTMLPurifier/DefinitionCache/Null.php

@@ -0,0 +1,76 @@
+<?php
+
+/**
+ * Null cache object to use when no caching is on.
+ */
+class HTMLPurifier_DefinitionCache_Null extends HTMLPurifier_DefinitionCache
+{
+
+    /**
+     * @param HTMLPurifier_Definition $def
+     * @param HTMLPurifier_Config $config
+     * @return bool
+     */
+    public function add($def, $config)
+    {
+        return false;
+    }
+
+    /**
+     * @param HTMLPurifier_Definition $def
+     * @param HTMLPurifier_Config $config
+     * @return bool
+     */
+    public function set($def, $config)
+    {
+        return false;
+    }
+
+    /**
+     * @param HTMLPurifier_Definition $def
+     * @param HTMLPurifier_Config $config
+     * @return bool
+     */
+    public function replace($def, $config)
+    {
+        return false;
+    }
+
+    /**
+     * @param HTMLPurifier_Config $config
+     * @return bool
+     */
+    public function remove($config)
+    {
+        return false;
+    }
+
+    /**
+     * @param HTMLPurifier_Config $config
+     * @return bool
+     */
+    public function get($config)
+    {
+        return false;
+    }
+
+    /**
+     * @param HTMLPurifier_Config $config
+     * @return bool
+     */
+    public function flush($config)
+    {
+        return false;
+    }
+
+    /**
+     * @param HTMLPurifier_Config $config
+     * @return bool
+     */
+    public function cleanup($config)
+    {
+        return false;
+    }
+}
+
+// vim: et sw=4 sts=4