Imputing missing values when computing distances
Data imputation on distances is performed only when needed by Distances widget
Sort by predicted values in Predictions widget
Fixed tree tests using multinomial attributes with scikit-learn methods.
Merge pull request #180 from thocevar/tree

Fixed tree tests using multinomial attributes with scikit-learn methods.
Leave the original data intact when imputing values for distance computation.
Merge pull request #177 from marinkaz/distances

Imputing missing values when computing distances.
Restore original order in Predictions widget.
Hides sort indicator for unsorted ordering in Predictions widget.
Merge pull request #179 from thocevar/predictions

Sort by predicted values in Predictions widget
Supported numpy arrays as inputs for distances.
Handling e1, e2 separately. Implemented extension ob basic classes.