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



This is the same as gh-2029 but rebased onto develop.

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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 http://trac.openmicroscopy.org.uk/ome/ticket/11850.  In the test case outlined in the ticket, the import times should now be roughly similar for the original file and the exported OME-TIFF.

Whether or not we really want to use 128x128 as the tile size across the board is up for debate, but it seemed like a reasonable value to use for now.