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/Token/End.php

@@ -0,0 +1,24 @@
+<?php
+
+/**
+ * Concrete end token class.
+ *
+ * @warning This class accepts attributes even though end tags cannot. This
+ * is for optimization reasons, as under normal circumstances, the Lexers
+ * do not pass attributes.
+ */
+class HTMLPurifier_Token_End extends HTMLPurifier_Token_Tag
+{
+    /**
+     * Token that started this node.
+     * Added by MakeWellFormed. Please do not edit this!
+     * @type HTMLPurifier_Token
+     */
+    public $start;
+
+    public function toNode() {
+        throw new Exception("HTMLPurifier_Token_End->toNode not supported!");
+    }
+}
+
+// vim: et sw=4 sts=4