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/Definition.php

@@ -0,0 +1,55 @@
+<?php
+
+/**
+ * Super-class for definition datatype objects, implements serialization
+ * functions for the class.
+ */
+abstract class HTMLPurifier_Definition
+{
+
+    /**
+     * Has setup() been called yet?
+     * @type bool
+     */
+    public $setup = false;
+
+    /**
+     * If true, write out the final definition object to the cache after
+     * setup.  This will be true only if all invocations to get a raw
+     * definition object are also optimized.  This does not cause file
+     * system thrashing because on subsequent calls the cached object
+     * is used and any writes to the raw definition object are short
+     * circuited.  See enduser-customize.html for the high-level
+     * picture.
+     * @type bool
+     */
+    public $optimized = null;
+
+    /**
+     * What type of definition is it?
+     * @type string
+     */
+    public $type;
+
+    /**
+     * Sets up the definition object into the final form, something
+     * not done by the constructor
+     * @param HTMLPurifier_Config $config
+     */
+    abstract protected function doSetup($config);
+
+    /**
+     * Setup function that aborts if already setup
+     * @param HTMLPurifier_Config $config
+     */
+    public function setup($config)
+    {
+        if ($this->setup) {
+            return;
+        }
+        $this->setup = true;
+        $this->doSetup($config);
+    }
+}
+
+// vim: et sw=4 sts=4