expand form options to support only on updates or only on creates

[MikeCarbone]

We need flexibility to discern whether this field is available only on creates or updates.

For example, maybe you want some field hidden on create but not on update, like an id.

maybe

form: {
  hidden: true 
  // or
  hidden: {
    on_create: true | false,
    on_update: true | false
  }
}