Interactive unfold while exporting

[addam]

While the export is running (user sees the file browser), it should be possible to modify Scale or Limit Islands Size setting and get a new unfold, instantly.

The results will not be directly visible but it should enable a much cleaner workflow. Scale and Page Size settings are now duplicated in 3D View which must be confusing to users and positively is annoying to manage for the developer (myself).

Downside is that these settings may perhaps need to be resurrected later and placed in Unfold operator settings -- so as to allow customization of the folds properly.