Improve list level unsubscribe stats

We want to show admin how many subscribers subscribed to a list and how many
unsubscribed within last 30 days so that they see the change.
If someone subscribed and also unsubscribed within those 30 days we skip him.
We don't have data to detect they were really subscribed at some point.
[MAILPOET-4828]

mailpoet/lib/Subscribers/SubscribersRepository.php

@@ -432,6 +432,7 @@ class SubscribersRepository extends Repository {
       ->join('ss.subscriber', 's')
       ->join('ss.segment', 'seg')
       ->where('ss.updatedAt > :date')
+      ->where('ss.createdAt < :date') // ignore those who subscribed and unsubscribed within the date range
       ->andWhere('s.status = :status')
       ->andWhere('ss.status = :segment_status')
       ->andWhere('s.deletedAt IS NULL')