Make user account a property of a pad, not a method parameter

It's kind of crazy to be passing around an account object for a pad object. Instead, we should just set it when creating or loading the pad. Since I can't think of a use case to load a pad as one user, and then save it as another during the same page request, I've left out set / get methods. Of course, the property is public, so it can be changed if needed.