go-unityscopes v2 lacks some useful functions

1.We now are not able to use the following functions just like the way we use in C++
  - setUserData()
  - Userdata()
  - HasUserdata()

2. Also no way to push widgets list over []PreviewWidget which makes it harder to push widgets in some cases in elegant way.
e.g. reply.PushWidgetsList(widget1, widget2, widget3..... widget100)

The following way may look better
widgets := make([]scopes.PreviewWidget, 0)

for index := 100; index >= 0; index-- {
     comment := scopes.NewPreviewWidget("comment"+strconv.Itoa(index), "comment")
     ....
     widgets = append(widgets, comment)
}

reply.PushWidgetsList(widgets)