filter subscriptions pretend to work happily even when there is no configured mail server

Users can create filter subscriptions, can click "run now" and the last sent and next send are shown - even if there is no mail server configured in the system.

Additionally, the mail queue gets an email in it which will never be sent until a mail sever is added.

The user should not be able to edit or run filter subscriptions (and they should not attempt to run or enqueue emails). The user should not be given the impression that email will be or has been sent.