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/CSS/Composite.php

@@ -0,0 +1,48 @@
+<?php
+
+/**
+ * Allows multiple validators to attempt to validate attribute.
+ *
+ * Composite is just what it sounds like: a composite of many validators.
+ * This means that multiple HTMLPurifier_AttrDef objects will have a whack
+ * at the string.  If one of them passes, that's what is returned.  This is
+ * especially useful for CSS values, which often are a choice between
+ * an enumerated set of predefined values or a flexible data type.
+ */
+class HTMLPurifier_AttrDef_CSS_Composite extends HTMLPurifier_AttrDef
+{
+
+    /**
+     * List of objects that may process strings.
+     * @type HTMLPurifier_AttrDef[]
+     * @todo Make protected
+     */
+    public $defs;
+
+    /**
+     * @param HTMLPurifier_AttrDef[] $defs List of HTMLPurifier_AttrDef objects
+     */
+    public function __construct($defs)
+    {
+        $this->defs = $defs;
+    }
+
+    /**
+     * @param string $string
+     * @param HTMLPurifier_Config $config
+     * @param HTMLPurifier_Context $context
+     * @return bool|string
+     */
+    public function validate($string, $config, $context)
+    {
+        foreach ($this->defs as $i => $def) {
+            $result = $this->defs[$i]->validate($string, $config, $context);
+            if ($result !== false) {
+                return $result;
+            }
+        }
+        return false;
+    }
+}
+
+// vim: et sw=4 sts=4