Allow to restrict the users which see the create forum form

A new forum can be created from the page Forums.WebHome with a form. Now, the issue is that a new forum means a new space, so as long as Forums.WebHome is accessivle to the user and as long as they have the right to create a new space (a new page) on the wiki, they can create a new forum. It is not always acceptable to remove users the right to create new spaces on the wiki.

A mid way to that is to be able to configure who sees the forum creation form, even if they can see the list of forums, or even if otherwise they would be able to create a new space on the wiki.
This would not mean that they cannot create a forum (since they can always create a new space and put an object on the webhome), it will only prevent the form to be visible for regular simple users.