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/Node.php

@@ -0,0 +1,49 @@
+<?php
+
+/**
+ * Abstract base node class that all others inherit from.
+ *
+ * Why do we not use the DOM extension?  (1) It is not always available,
+ * (2) it has funny constraints on the data it can represent,
+ * whereas we want a maximally flexible representation, and (3) its
+ * interface is a bit cumbersome.
+ */
+abstract class HTMLPurifier_Node
+{
+    /**
+     * Line number of the start token in the source document
+     * @type int
+     */
+    public $line;
+
+    /**
+     * Column number of the start token in the source document. Null if unknown.
+     * @type int
+     */
+    public $col;
+
+    /**
+     * Lookup array of processing that this token is exempt from.
+     * Currently, valid values are "ValidateAttributes".
+     * @type array
+     */
+    public $armor = array();
+
+    /**
+     * When true, this node should be ignored as non-existent.
+     *
+     * Who is responsible for ignoring dead nodes?  FixNesting is
+     * responsible for removing them before passing on to child
+     * validators.
+     */
+    public $dead = false;
+
+    /**
+     * Returns a pair of start and end tokens, where the end token
+     * is null if it is not necessary. Does not include children.
+     * @type array
+     */
+    abstract public function toTokenPair();
+}
+
+// vim: et sw=4 sts=4