Move signup node type settings out of "workflow" into "Signup settings"

One of the things I did over at #335563-2: allow admins to specify weight for the signup info on nodes was to move the signup-related settings on the node type configure page out of the "Workflow" fieldset into a separate "Signup settings" fieldset. That seems worth doing, even though the rest of that monster patch has been cut down. We've already got the signup radios, and on CCK sites, the "Date field to use with signup" setting. We're probably going to have more in the future, e.g. for #335749: Make "Location of signup form" setting per node-type, not site-wide, #290249: Make autoclose time per-node, not just site-wide, and probably for some of the stuff from #290305: Split out email functionality into separate submodule(s), too....