Dual mode MS2Deepscore model

An MS2Deepscore model trained on both positive and negative ionisation mode spectra. It is suitable to predict chemical similarity between two mass spectra, both between the same ionmode, but also between positive and negative ion mode spectra. See https://github.com/matchms/ms2deepscore for more details. 

This new version is trained with a new training algorithm resulting in improved model performance. 

In addition a embedding evaluator model has been added. This model is not necessary for running MS2Deepscore, but can be used to estimate the prediction error for the embedding of a spectrum, this can help to filter out spectra with low information content, which will likely get unreliable MS2Deepscore predictions.