Manage subscriptions

- make use of the SubscriberSegment::status column to keep track of unsubscriptions
- unsubscribed segments now appear grayed out in the Subscribers listing
- added unsubscribed_at after segment names when editing a subscriber
- added date() method for Twig (uses WP's date format / date_offset)
- fixed typo in Form iframe export
- fixed unit test for Newsletters
- updated selection component (JSX) to allow more customization

lib/Listing/Handler.php

@@ -89,7 +89,7 @@ class Handler {
     $items = $this->model
       ->offset($this->data['offset'])
       ->limit($this->data['limit'])
-      ->findArray();
+      ->findMany();
 
     return array(
       'count' => $count,