- gpu implementation via Qt6 for generic graphics card (Nvidia, AMD, Intel).
  Performance is not super critical here. We just want something faster
  with focus on ease of programming.
- integer arithmetic for translation (and cage) so that image in 
  live viewer always uses the same output canvas as the input image
  (without partial voxels). Upgrade old json file (via --save-json).
- opacity effects of editing layers with background image to see
  overlap, if any.
- highlight operations in Undo Stack for the layer being selected.
- in Docks, draw a coloured box (not gray on black) around the 
  selection checkmark.
- upgrade json project files for sections that we repaired with 
  Hartmut's first version of ImageEditor on the Mac (I think this
  was the pre-Qt6 version). Ensure compatibility with the new Qt6
  based version. Regenerate those repaired images using masking.
- export variable in config file for point size and line thickness
  when drawing a polygon. The line thickness can be hardcoded to
  half the radius of the control point.
 
Aug 21:
- fix documentation on github page for Windows with WSL for Ubuntu24.
  Fix the formatting. Add newlines, maybe bullet style to look the
  same as WSL for Debian.