(VC) Add support for algorithms which propagate in -Z

[csparker247]

I recommend updating this function as well. added bonus: -Compatible with backwards segmentation -Not deleting segmentation process above current segmentation job -Displaying target segmentation layer when finishing the segmentation job.

void CWindow::onSegmentationFinished(Segmenter::PointSet ps)
{
    setWidgetsEnabled(true);
    worker_progress_updater_.stop();
    worker_progress_.close();
    // 3) concatenate the two parts to form the complete point cloud
    // find starting location in fMasterCloud
    int i;
    for (i= 0; i < fMasterCloud.height(); i++) {
        auto masterRowI = fMasterCloud.getRow(i);
        if (ps[0][2] <= masterRowI[fUpperPart.width()-1][2]){
            break;
        }
    }

    // remove the duplicated point and ps in their stead. if i at the end, no duplicated point, just append
    fUpperPart = fMasterCloud.copyRows(0, i);
    fUpperPart.append(ps);

    // check if remaining rows already exist in fMasterCloud behind ps
    for(; i < fMasterCloud.height(); i++) {
        auto masterRowI = fMasterCloud.getRow(i);
        if (ps[ps.size() - 1][2] < masterRowI[fUpperPart.width()-1][2]) {
            break;
        }
    }
    // add the remaining rows
    if (i < fMasterCloud.height()) {
        fUpperPart.append(fMasterCloud.copyRows(i, fMasterCloud.height()));
    }

    fMasterCloud = fUpperPart;

    statusBar->showMessage(tr("Segmentation complete"));
    fVpkgChanged = true;

    // set display to target layer
    fPathOnSliceIndex = fSegParams.targetIndex;
    CleanupSegmentation();
    UpdateView();
}

Originally posted by @schillij95 in https://github.com/educelab/volume-cartographer/issues/25#issuecomment-1553691083

[csparker247]

I'm not sure if this is the way we ultimately want to approach this problem, but it's a start. The parts about removing duplicated points should be irrelevant after #25 is merged.