replaced mailer library, added email templates (#1462)

src/Configuration/MailConfiguration.php

@@ -0,0 +1,24 @@
+<?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 MailConfiguration
+{
+    public function getFromAddress(): ?string
+    {
+        $from = getenv('MAILER_FROM');
+
+        if ($from === false || empty($from)) {
+            return null;
+        }
+
+        return $from;
+    }
+}