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/ChildDef.php

@@ -0,0 +1,52 @@
+<?php
+
+/**
+ * Defines allowed child nodes and validates nodes against it.
+ */
+abstract class HTMLPurifier_ChildDef
+{
+    /**
+     * Type of child definition, usually right-most part of class name lowercase.
+     * Used occasionally in terms of context.
+     * @type string
+     */
+    public $type;
+
+    /**
+     * Indicates whether or not an empty array of children is okay.
+     *
+     * This is necessary for redundant checking when changes affecting
+     * a child node may cause a parent node to now be disallowed.
+     * @type bool
+     */
+    public $allow_empty;
+
+    /**
+     * Lookup array of all elements that this definition could possibly allow.
+     * @type array
+     */
+    public $elements = array();
+
+    /**
+     * Get lookup of tag names that should not close this element automatically.
+     * All other elements will do so.
+     * @param HTMLPurifier_Config $config HTMLPurifier_Config object
+     * @return array
+     */
+    public function getAllowedElements($config)
+    {
+        return $this->elements;
+    }
+
+    /**
+     * Validates nodes according to definition and returns modification.
+     *
+     * @param HTMLPurifier_Node[] $children Array of HTMLPurifier_Node
+     * @param HTMLPurifier_Config $config HTMLPurifier_Config object
+     * @param HTMLPurifier_Context $context HTMLPurifier_Context object
+     * @return bool|array true to leave nodes as is, false to remove parent node, array of replacement children
+     */
+    abstract public function validateChildren($children, $config, $context);
+}
+
+// vim: et sw=4 sts=4