Ability to be notified about posted comments

From ticket #5 on the Campware Trac:

https://www.campware.org/projects/campware/ticket/5

It would be very good to get a system of notifications working for new comments posts by both e-mail (probably best handled by existing Phorum notifications) or by an RSS feed for new comments.

Ideally, the system would allow for responses to be sent via e-mail as well, and the e-mailed response would automatically be added to the article in question.

If we wanted to be _really_ slick, we could make it be governed by the “User will be informed on several events” checkbox ;-))))

E-mailed notification for new comments should be added to the list of user type permissions.

At the same time, any site visitor who submits a comment should be notified by e-mail of additional comments to the thread. This behavior should be enabled by default, but should also be configurable in the system preferences:

Notify users about new comments in a thread? [x]