- Refactors sending queue worker by breaking it into smaller tasks

- Adds arrayUnique method to Helpers for multidimensional arrays

lib/Cron/Workers/SendingQueue/Tasks/Shortcodes.php

@@ -0,0 +1,14 @@
+<?php
+namespace MailPoet\Cron\Workers\SendingQueue\Tasks;
+
+use MailPoet\Newsletter\Shortcodes\Shortcodes as NewsletterShortcodes;
+
+if(!defined('ABSPATH')) exit;
+
+class Shortcodes {
+  static function process($content, array $newsletter, array $subscriber, array $queue) {
+    $shortcodes = new NewsletterShortcodes($newsletter, $subscriber, $queue);
+    return $shortcodes->replace($content);
+  }
+}
+