Enable long format for .csv output

[ArtemSokolov]

Allow MCquant to write .csv files in "long" format, which can capture multiple masks, metrics, background subtraction methods, etc.:

CellID,Background,Transform,Metric,Mask,CD3,CD45,CD8,...
1,none,raw,mean,cell,...
1,rollball,raw,mean,cell,...
1,none,log,mean,cell,...
1,none,log,gini,cell,...
1,none,log,gini,nuclei,...

This will produce multiple rows for each cell but preserve direct matching of column names against markers.csv. To avoid unnecessary duplication of morphological features, they can be written to a separate file.