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/AttrDef/Switch.php

@@ -0,0 +1,53 @@
+<?php
+
+/**
+ * Decorator that, depending on a token, switches between two definitions.
+ */
+class HTMLPurifier_AttrDef_Switch
+{
+
+    /**
+     * @type string
+     */
+    protected $tag;
+
+    /**
+     * @type HTMLPurifier_AttrDef
+     */
+    protected $withTag;
+
+    /**
+     * @type HTMLPurifier_AttrDef
+     */
+    protected $withoutTag;
+
+    /**
+     * @param string $tag Tag name to switch upon
+     * @param HTMLPurifier_AttrDef $with_tag Call if token matches tag
+     * @param HTMLPurifier_AttrDef $without_tag Call if token doesn't match, or there is no token
+     */
+    public function __construct($tag, $with_tag, $without_tag)
+    {
+        $this->tag = $tag;
+        $this->withTag = $with_tag;
+        $this->withoutTag = $without_tag;
+    }
+
+    /**
+     * @param string $string
+     * @param HTMLPurifier_Config $config
+     * @param HTMLPurifier_Context $context
+     * @return bool|string
+     */
+    public function validate($string, $config, $context)
+    {
+        $token = $context->get('CurrentToken', true);
+        if (!$token || $token->name !== $this->tag) {
+            return $this->withoutTag->validate($string, $config, $context);
+        } else {
+            return $this->withTag->validate($string, $config, $context);
+        }
+    }
+}
+
+// vim: et sw=4 sts=4