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/Models/Subscriber.php

@@ -291,7 +291,7 @@ class Subscriber extends Model {
         }
       }
       if($segment_ids !== false) {
-        $subscriber->addToSegments($segment_ids);
+        SubscriberSegment::setSubscriptions($subscriber, $segment_ids);
       }
     }
     return $subscriber;
@@ -314,6 +314,17 @@ class Subscriber extends Model {
     return $this;
   }
 
+  function withSegments() {
+    $this->segments = $this->segments()->findArray();
+    return $this;
+  }
+
+  function withSubscriptions() {
+    $this->subscriptions = SubscriberSegment::where('subscriber_id', $this->id())
+      ->findArray();
+    return $this;
+  }
+
   function getCustomField($custom_field_id, $default = null) {
     $custom_field = SubscriberCustomField::select('value')
       ->where('custom_field_id', $custom_field_id)