added project importer and grandtotal converter (#1468)

src/Importer/ImportReaderInterface.php

@@ -0,0 +1,20 @@
+<?php
+
+/*
+ * This file is part of the Kimai time-tracking app.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace App\Importer;
+
+interface ImportReaderInterface
+{
+    /**
+     * @param string $input
+     * @return \Iterator
+     * @throws ImportNotFoundException
+     */
+    public function read(string $input): \Iterator;
+}