Progress report of the writing of N5ScalePyramidExporter

[tischi]

I think, and there was another user request, that it would be good for the UX if there was some written progress report, such as when saving BDV/XML from BDV:

starting export...
proccessing timepoint 1 / 1
proccessing setup 1 / 1
writing level 0
done

Otherwise when saving big data one does not really know the status and might think it has crashed.

What do you think?