renaming fields moves them to the bottom of the form

This looks like a side effect of the fix for #88. It happens only for fields that haven't been reordered (i.e. when there is no defined ui:order) so the fix might be to always include a ui:order by default. Prior to the mentioned change in fact the ui:order was not being set by default but it was being set on rename, whereas now it's not set on rename, only on reorder.