Make form privacy setting available in document and some other improvements

In Coda forms there is a privacy setting to allow submissions.

It would be nice if we could set this switch with a webhook, or from a switch in our document preferably in any document, but in the originating document would be OK too).

If submissions are not allowed, the submit button should not be visible either or have a custom text in this box. The button should also not act as if the submission is made, which currently is very confusing.