segmentation.py: adaptation to allow usage of OpenCV 4.0 alongside 3.4

editParticles.py: correctly handle cancelation of Combine and Reassign actions; adaptation to allow usage of OpenCV 4.0 alongside 3.4
analysisview.py: some first restructuring; export dialogs are now QDialogs instead of QWidgets; restructuring of ExcelExport and bugfixes therein; hit quality index export is broken and now set to zero instead wrong numbers