Changes:
- added isFitValid() method in Func1D for returning MINUIT FunctionMinimum.isValid() result.
- user can change the format string used to display function parameters in stat box.
- Fixed the issue with TDirectory changing dataset name to canonical while saving.
- fixed the crash when GraphErrors is saved without any points
- added dynamic resizing of the event in tdirectory save (there was an issue with saving large 2d histograms)