Editing/deleting status page update subscribers#228

Currently it is only possible to see how many subscribers a status page has, and to delete them all. It would be nice to be able to view and delete individual emails from the list. Two use cases:

1) In communication with a customer, it may be good to know if they’re subscribed to status updates or not.

2) When a user requests GDPR-based deletion of personal data, we should be able to delete them from the subscribers list.