added database driven system configurations with admin screen (#647)

src/Configuration/SystemConfiguration.php

@@ -0,0 +1,25 @@
+<?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\Configuration;
+
+class SystemConfiguration implements SystemBundleConfiguration
+{
+    use StringAccessibleConfigTrait;
+
+    public function getPrefix(): string
+    {
+        return 'kimai';
+    }
+
+    protected function getConfigurations(ConfigLoaderInterface $repository): array
+    {
+        return $repository->getConfiguration();
+    }
+}