Feature Constructor: allow creating meta variables directly

[markotoplak]

What's your use case? Sometimes a user wants to construct a numeric feature that is not used for modeling but only for display. I needed that feature quite a few times.

What's your proposed solution? A user could choose where to put the feature (attributes, metas, classes) in the Feature constructor. That would require an additional combo box.

Are there any alternative solutions? Currently, a Select Columns can be used after Feature Constructor to move the feature.

[janezd]

In discussion, we said that classes may not be the most useful place (also because we discourage having multiple classes). This allows for using a (lighter) checkbox instead of a (heavier) combo.

I would suggest that the list contains only an indicator of where the variable will go. For changing it, the user would need to select the row and click the checkbox. This is consistent with how the widget works currently.

(In the future, the widget may be changed so that all editing is done within the table.)