[IMP] form_view: statusbar widget: folded back as an option.

The widget option 'fold_field' allows to tell the widget to use this field on
the model used for stages to compute the folded selection.

If not set, no stage is folded.
[IMP] form_view: statusbar widget: folded back as an option.

The widget option 'fold_field' allows to tell the widget to use this field on
the model used for stages to compute the folded selection.

If not set, no stage is folded.