added project importer and grandtotal converter (#1468)

src/Importer/CustomerImporterInterface.php

@@ -0,0 +1,17 @@
+<?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;
+
+use App\Entity\Customer;
+
+interface CustomerImporterInterface
+{
+    public function convertEntryToCustomer(array $entry): Customer;
+}