CellWorx: ignore thumbnails and missing channel names

Any TIFF files with "_thumb_" in the name are now ignored, so that
thumbnails are not inadvertently picked up.  If channel names are
missing from the .htd file, then the channel names stored in the
.pnl/.tif files will be used instead.
merge dev_4_4 -D org -I include -E exclude: PR 673 (Make configuration file suffix configurable)
merge dev_4_4 -D org -I include -E exclude: PR 710 (Data test updates (rebased onto dev_4_4))
merge dev_4_4 -D org -I include -E exclude: PR 746 (CellWorx: ignore thumbnails and missing channel names)