allow posts in multiple courses

[kohlhase]

We have forum posts associated to forums via their groups (If I remember correctly). So it should be possible to associate a post to multiple forums. For instance the post http://panta.kwarc.info/question/99 which was made on the GenCS forum originally, I would like to add to the TDM forum as well (I will drop the reference to GenCS, but that is very possible). I would like to have an interface that allows a person who has access to both courses to "adopt this post in another course". In the background this would only change groups and make it magically appear in the other forum as well. The same should be done with answers.

This is a new way of cross-posting which I feel would make my life as a instructor of multiple courses quite a lot easier. For the moment, I am copying the contents of the posts, which is less good.

This would be good to have for the new semester.