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/HTMLModule/Target.php

@@ -0,0 +1,28 @@
+<?php
+
+/**
+ * XHTML 1.1 Target Module, defines target attribute in link elements.
+ */
+class HTMLPurifier_HTMLModule_Target extends HTMLPurifier_HTMLModule
+{
+    /**
+     * @type string
+     */
+    public $name = 'Target';
+
+    /**
+     * @param HTMLPurifier_Config $config
+     */
+    public function setup($config)
+    {
+        $elements = array('a');
+        foreach ($elements as $name) {
+            $e = $this->addBlankElement($name);
+            $e->attr = array(
+                'target' => new HTMLPurifier_AttrDef_HTML_FrameTarget()
+            );
+        }
+    }
+}
+
+// vim: et sw=4 sts=4