re #19385: first version of PNG import

works for size <= 128px
re #19385: fill gaps between neighbourhood voxels
re #19385: use right neighbour voxels
re #19385: importing voxels should be destructive
re #19385: add hot-fix to allow import of big PNGs

sendVoxelsOperation() is sending data too fast, printf slows it down.
Better fix is required.
re #19385: use righ axis name
re #19385: CR changes
Merge remote-tracking branch 'worklist/master' into 19385
Merge pull request #607 from heracek/19385

Code Review for Job #19385