allow different status to be available to different permissions

Suggested by realEuph over at #227643-3: Allow each node to specify which status values should appear on its signup form :

allow different status to be available to different permissions. For example, an anonymous users only gets ;Registered' and 'Wait List', while an authenticated user also gets 'Priority'. This would be controlled on the signup_status admin page.

This is something that is important to me and I am willing to work on it. Contact me if interested.

That's really a whole different feature than #227643 so let's discuss/implement it here in its own issue.

Thanks,
-Derek