- Isolates shortcodes regex into a class method

- Adds a new method to create a URL data object as a numeric array instead
  of associative, thus reducing the size of the object
- Adds a new method to convert numeric URL data object array into associative
  array
- Preserves backward compatibility with previous MP3 Beta versions
  by checking if the URL data object is already an associative array

lib/Router/Endpoints/Track.php

@@ -5,6 +5,7 @@ use MailPoet\Models\Newsletter;
 use MailPoet\Models\NewsletterLink;
 use MailPoet\Models\SendingQueue;
 use MailPoet\Models\Subscriber;
+use MailPoet\Newsletter\Links\Links;
 use MailPoet\Statistics\Track\Clicks;
 use MailPoet\Statistics\Track\Opens;
 
@@ -35,10 +36,10 @@ class Track {
   }
 
   function _processTrackData($data) {
-    $data = (object)$data;
+    $data = (object)Links::transformUrlDataObject($data);
     if(empty($data->queue_id) ||
-      empty($data->subscriber_id) ||
-      empty($data->subscriber_token)
+       empty($data->subscriber_id) ||
+       empty($data->subscriber_token)
     ) {
       return false;
     }