Add anti-CSRF token

phpcs-errors:238 phpunit-status:successful

index.php

@@ -43,6 +43,7 @@ echo '
 
 <div class="uploader">
     <form enctype="multipart/form-data" action="upload.php" method="POST">
+        <input type="hidden" id="csrf-token" name="csrf-token" aria-label="Anti-CSRF Token" value="' . htmlspecialchars(getAntiCsrfToken()) . '" />
         <label for="fileToUpload">' . $csvxml_overview['select_csv_file_for_upload'] . '</label>
         <input name="uploaded" type="file" accept=".csv" id="fileToUpload" required />
         <button type="submit">' . $csvxml_overview['upload'] . '</button>