Make the "user set a profile picture" notification opt-in

[danielkrajnik]

I think that "'USERNAME' set a profile picture" notification should be an opt-in instead of opt-out as it is now. I'm not sure what advantage the current default brings? It definitely can be a bit embarrassing on a forum when an important discussion is going on and in the middle this notification "user set a profile picture" comes up. Especially when you joined a lot of different rooms and they all receive it.

Follow up to this issue.