#13 display multiple variograms

[Jianbing]

Sometimes, the user wants to compare the variograms from different realizations in one single plot (as in gslib).

Would it be possible to have a new sub-menu to allow the user to load multiple variogram data files, and put the variograms in the same direction into one single plot for the comparison purpose?

The other solution would be "to add the new loaded experimental variograms into the current variogram plots, instead of to clear the current variogram plots".