Composer: Add vendor directry

- Add gitignore to avoid committing libraries' .git folder

vendor/composer/autoload_psr4.php

@@ -0,0 +1,10 @@
+<?php
+
+// autoload_psr4.php @generated by Composer
+
+$vendorDir = dirname(dirname(__FILE__));
+$baseDir = dirname($vendorDir);
+
+return array(
+    'Friendica\\' => array($baseDir . '/include'),
+);