- Refactors sending queue worker by breaking it into smaller tasks

- Adds arrayUnique method to Helpers for multidimensional arrays

lib/Newsletter/Renderer/PostProcess/OpenTracking.php

@@ -8,12 +8,18 @@ class OpenTracking {
     $DOM = new \pQuery();
     $DOM = $DOM->parseStr($template);
     $template = $DOM->query('body');
-    $open_tracking_link = sprintf(
+    $open_tracking_image = sprintf(
       '<img alt="" class="" src="%s/%s"/>',
       home_url(),
       esc_attr('?mailpoet&endpoint=track&action=open&data=' . Links::DATA_TAG)
     );
-    $template->html($template->html() . $open_tracking_link);
+    $template->html($template->html() . $open_tracking_image);
     return $DOM->__toString();
   }
+
+  static function addTrackingImage() {
+    add_filter('mailpoet_rendering_post_process', function ($template) {
+      return OpenTracking::process($template);
+    });
+  }
 }