[Python] Use `weights` in Permutation Feature Importance calculation

[danielarifmurphy]

Hi Dalex team - great job on the package!

I am looking to use sample weights when using PFI. Whilst we can pass weights to the Explainer, it is not currently used in the loss calculation at each permutation round.

Could we open up the loss_function to take sample weights as optional argument?

[hbaniecki]

Thank you for contributing to dalex