Refactor emails models objects, rework related tests

common/emails/exceptions/CannotRenderEmailException.php

@@ -0,0 +1,15 @@
+<?php
+declare(strict_types=1);
+
+namespace common\emails\exceptions;
+
+use Exception;
+use Throwable;
+
+class CannotRenderEmailException extends Exception {
+
+    public function __construct(Throwable $previous = null) {
+        parent::__construct('Unable to render a template', 0, $previous);
+    }
+
+}