fix: Adapt copyToQImage for greyscale images

d.kilicrequested to merge
338-greyscale-image-sequence-not-visable into master

Issues with handling greyscale sequences were only in the visualization.

The copyToQImage method did not handle greyscale images correctly. This was fixed, by repacing the handmade loop with a constructor of QImage.

Closes #338 (closed)

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