Add beeswarm plot

[nilchia]

It is a cool plot to show the feature importance.

The idea is to implement something similar to this in the SHAP package:

The beeswarm plot is designed to display an information-dense summary of how the top features in a dataset impact the model’s output. Each instance the given explanation is represented by a single dot on each feature row. The x position of the dot is determined by the SHAP value (shap_values.value[instance,feature]) of that feature, and dots “pile up” along each feature row to show density. Color is used to display the original value of a feature (shap_values.data[instance,feature]). In the plot below we can see that Age is the most important feature on average, and than young (blue) people are less likely to make over $50k.

Requested by: @gdefazio
ping: @borauyar @bgruening
assigned to @nilchia

[borauyar]

@nilchia sure, feel free to add a function in utils.py

[nilchia]

first attemp gives sth like this:

I'll add another function for flexynesis feature importance. The beeswarp is good for shap package where there is an importance value for each feature per sample.