Forum subscription

Have done some work to let users be able to subscribe to a particular forum, the user gets email on any post to that forum. 

It also has a switch in the Forum Holder->settings page to be able to let the Administrator decided if they will have that function. I added a field in the settings to let the admin decide which email address it should come from.

have modified the configuration about how to use the switch and email address

Why not implement this as a many_many relationship and use extraFields to store the LastSent?