Refactor emails models objects, rework related tests

common/emails/RendererInterface.php

@@ -0,0 +1,10 @@
+<?php
+declare(strict_types=1);
+
+namespace common\emails;
+
+interface RendererInterface {
+
+    public function render(string $templateName, string $locale, array $params = []): string;
+
+}