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/Presentation.php

@@ -0,0 +1,42 @@
+<?php
+
+/**
+ * XHTML 1.1 Presentation Module, defines simple presentation-related
+ * markup. Text Extension Module.
+ * @note The official XML Schema and DTD specs further divide this into
+ *       two modules:
+ *          - Block Presentation (hr)
+ *          - Inline Presentation (b, big, i, small, sub, sup, tt)
+ *       We have chosen not to heed this distinction, as content_sets
+ *       provides satisfactory disambiguation.
+ */
+class HTMLPurifier_HTMLModule_Presentation extends HTMLPurifier_HTMLModule
+{
+
+    /**
+     * @type string
+     */
+    public $name = 'Presentation';
+
+    /**
+     * @param HTMLPurifier_Config $config
+     */
+    public function setup($config)
+    {
+        $this->addElement('hr', 'Block', 'Empty', 'Common');
+        $this->addElement('sub', 'Inline', 'Inline', 'Common');
+        $this->addElement('sup', 'Inline', 'Inline', 'Common');
+        $b = $this->addElement('b', 'Inline', 'Inline', 'Common');
+        $b->formatting = true;
+        $big = $this->addElement('big', 'Inline', 'Inline', 'Common');
+        $big->formatting = true;
+        $i = $this->addElement('i', 'Inline', 'Inline', 'Common');
+        $i->formatting = true;
+        $small = $this->addElement('small', 'Inline', 'Inline', 'Common');
+        $small->formatting = true;
+        $tt = $this->addElement('tt', 'Inline', 'Inline', 'Common');
+        $tt->formatting = true;
+    }
+}
+
+// vim: et sw=4 sts=4