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/AttrTransform/NameSync.php

@@ -0,0 +1,41 @@
+<?php
+
+/**
+ * Post-transform that performs validation to the name attribute; if
+ * it is present with an equivalent id attribute, it is passed through;
+ * otherwise validation is performed.
+ */
+class HTMLPurifier_AttrTransform_NameSync extends HTMLPurifier_AttrTransform
+{
+
+    public function __construct()
+    {
+        $this->idDef = new HTMLPurifier_AttrDef_HTML_ID();
+    }
+
+    /**
+     * @param array $attr
+     * @param HTMLPurifier_Config $config
+     * @param HTMLPurifier_Context $context
+     * @return array
+     */
+    public function transform($attr, $config, $context)
+    {
+        if (!isset($attr['name'])) {
+            return $attr;
+        }
+        $name = $attr['name'];
+        if (isset($attr['id']) && $attr['id'] === $name) {
+            return $attr;
+        }
+        $result = $this->idDef->validate($name, $config, $context);
+        if ($result === false) {
+            unset($attr['name']);
+        } else {
+            $attr['name'] = $result;
+        }
+        return $attr;
+    }
+}
+
+// vim: et sw=4 sts=4