added annotation based exporter (#1831)

* added user exporter
* added project exporter
* added customer exporter
* added activity exporter

tests/Export/Spreadsheet/Entities/MissingExpressionOnClass.php

@@ -0,0 +1,19 @@
+<?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\Tests\Export\Spreadsheet\Entities;
+
+use App\Export\Annotation as Exporter;
+
+/**
+ * @Exporter\Expose("accessor", label="label.accessor")
+ */
+class MissingExpressionOnClass
+{
+}