maskGradient function added
createLinesFromXy moved to private
Added history of weights and foreground fixing if new foreground stroke
given

ProgressiveCut:
In connectNodes() added history and foreground fixing if updating
In updateGraph copied createGraph function, except fore connectNodes
arguments changed
Try to make work createLinesFromXy
QImage* strokeSelectionNew is now used for saveing new stroke

MainWindow:
buttonForegroundClicked() and buttonBackgroundClicked() now displaying
result of segmentation, after updating graph