suppress email notifications for defined groups

[JoergOswald]

Good Work!

It would be very cool and helpful if the plugin could be configured that
defined groups never get mails. The user has to be member of a
for example "Don't Spam me"-Group in that specific project for not
getting emails at all.

This would be perfect to have redmine users as responsible for Tickets,
which isn't controlled by the user itself, but by a project manager.
It helps keeping up with all issues. In this scenario, communication will be made
by email.

Thanks!