Changeset 11589 for branches/HeuristicLab.DatasetRefactor/sources/HeuristicLab.Problems.DataAnalysis/3.4/ModifiableDataset.cs

#2276: Unsealed Dataset class, refactored GetDoubleValues, GetStringValues, GetDateTimeValues methods to internally use the same generic method, added ModifiableDataset class which adds the functionality of replacing, adding or removing rows in the dataset.