TODO

1. When an anonymous user tries to subscribe / unsubscribe with an email 
address of a member, the anon user should be informed to log in as member
first to manage subscriptions.

2. When error 1 (mail template) occurs, that email should be sent to 
portal admin.

3. Can error 3 (mail template) actually happen?

4. Add feature to manually add subscribers to Subscriptions panel.
