ExporterI: set tile size for exported files to 128x128

This prevents the OME-TIFF writer from writing each row of pixels as a
separate strip, which should improve performance upon re-importing the
exported file.

See ticket #11850.
Merge pull request #2091 from joshmoore/rebased/develop/tile-export

ExporterI: set tile size for exported files to 128x128 (rebased onto develop)