It is the class_weight parameter.

Really? Which cache specifically? Because there doesn't seem to be one specifically for PubMed.

You would have to provide more information on what OS you are using and how you installed Orange.

I would just like to add that Orange usually wraps scikit-learn's models, so the same that applies for sklean would apply for Orange.

Basically, Frankstr summed it up quite nicely. I would only add that, if you will start creating a widget for stream data, have a look at EnKlik Anketa and Google Sheets image in Prototypes add-on, which both implement data reload, which simulates streaming.