text: Title: Path normalization (train on Windows and deploy on Linux)
  Body: I trained models on Windows, then I tried to use them on Linux, however, I could not load them due to an incorrect path joining. During model loading, I got `learner_path` in the following format `experiments_dir/model_1/100_LightGBM\\learner_fold_0.lightgbm`. The last two slashes were incorrectly concatenated with the rest part of the path. In this regard, I would suggest adding something like `learner_subpath = learner_subpath.replace("\\", "/")` before [this code line](https://github.com/mljar/mljar-supervised/blob/92706af75bd1859805a413768dc261d0572c3e06/supervised/model_framework.py#L590). Though, there is a need to think about opposite cases: when a model is trained on Linux and then is used on Windows. 
  