render a button to add/change the form while editing
returns
the empty string if there's no WEBFORM
or "Add form" if there is no form attached to a topic yet
or "Change form" otherwise
there are no native means besides the "addform" template being used
to render the FORMFIELDS. but this is not what we need here at all. infact
we need an empty addform.nat.tmp to switch off this feature of FORMFIELDS