ColortableImageRequest: Added an assert to check array dtype.
Removed Op5ifyer, which now lives in the lazyflow repo.
ImageScene2D: Updated prefetching bow wave generation for new defintion of tiling stack_id.
Revert "ImageScene2D: Updated prefetching bow wave generation for new defintion of tiling stack_id."

This reverts commit eb7995ecaa0c21efcf905156914d3c3c6de20f25.
tiling.py: Fixed creation of stack_id in prefetch()
exportDlg: Removed unused imports