registration update

Since only the admin can only make users figured I would add some stuff.
A user must have a user_level in order to use the site.
So, after creating a user an admin must (should) give that user a level
(admin, teller, or customer).
What happened in this patch is that two things happened.
First, during sign_up the admin session is no longer replaced.
Second, after sign_up the admin will be redirected to the user's show
page with buttons to give them a user_level.