Incremental training (retrain) support removed

[gabrielspmoreira]

Hi Balázs. I saw GRU4Rec had in an earlier version the retrain option, to keep fine tuning a model (i.e., multiple fit() calls) with newer data . I remember that feature created additional output neurons for item ids not seen in the previous training. Why was that option removed? Is that because the training accuracy is not good under such training approach? Or just to make the implementation simpler? I believe that retrain feature is important to avoid training runtime getting longer every day as new data becomes available.