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/BoolToCSS.php

@@ -0,0 +1,47 @@
+<?php
+
+/**
+ * Pre-transform that changes converts a boolean attribute to fixed CSS
+ */
+class HTMLPurifier_AttrTransform_BoolToCSS extends HTMLPurifier_AttrTransform
+{
+    /**
+     * Name of boolean attribute that is trigger.
+     * @type string
+     */
+    protected $attr;
+
+    /**
+     * CSS declarations to add to style, needs trailing semicolon.
+     * @type string
+     */
+    protected $css;
+
+    /**
+     * @param string $attr attribute name to convert from
+     * @param string $css CSS declarations to add to style (needs semicolon)
+     */
+    public function __construct($attr, $css)
+    {
+        $this->attr = $attr;
+        $this->css = $css;
+    }
+
+    /**
+     * @param array $attr
+     * @param HTMLPurifier_Config $config
+     * @param HTMLPurifier_Context $context
+     * @return array
+     */
+    public function transform($attr, $config, $context)
+    {
+        if (!isset($attr[$this->attr])) {
+            return $attr;
+        }
+        unset($attr[$this->attr]);
+        $this->prependCSS($attr, $this->css);
+        return $attr;
+    }
+}
+
+// vim: et sw=4 sts=4