Don't allow jpeg export of Big images

From http://trac.openmicroscopy.org.uk/ome/ticket/10841
For Big images, if we try to run Batch_Image_Export with any format, we should return a "Not supported" message.

This is simply an extension of https://github.com/ome/scripts/pull/30 to apply to ALL formats (not just OME-TIFF).

NB: haven't tested this locally because of issues with https://trac.openmicroscopy.org.uk/ome/ticket/10970

To test:
 - Try to run Batch_Image_Export.py with any Big image, choosing format as JPEG, then again with OME-TIFF.
 - Should get the same message with each.