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/AlphaValue.php

@@ -0,0 +1,34 @@
+<?php
+
+class HTMLPurifier_AttrDef_CSS_AlphaValue extends HTMLPurifier_AttrDef_CSS_Number
+{
+
+    public function __construct()
+    {
+        parent::__construct(false); // opacity is non-negative, but we will clamp it
+    }
+
+    /**
+     * @param string $number
+     * @param HTMLPurifier_Config $config
+     * @param HTMLPurifier_Context $context
+     * @return string
+     */
+    public function validate($number, $config, $context)
+    {
+        $result = parent::validate($number, $config, $context);
+        if ($result === false) {
+            return $result;
+        }
+        $float = (float)$result;
+        if ($float < 0.0) {
+            $result = '0';
+        }
+        if ($float > 1.0) {
+            $result = '1';
+        }
+        return $result;
+    }
+}
+
+// vim: et sw=4 sts=4