Add precision recall curve

[joshuawe]

We already have the receiver operating charcateristic curve and the corresponding AUROC.

We should also add the Precision recall curve: See here:

• https://scikit-learn.org/stable/auto_examples/model_selection/plot_precision_recall.html
• https://machinelearningmastery.com/roc-curves-and-precision-recall-curves-for-classification-in-python/

[FabianKruger]

I already have an implementation for it but it is not very beautiful yet. Let's see if I can improve it a bit

[FabianKruger]

Added the src code. Still needs an example plot.

[joshuawe]

• [x] example plot
• [x] include bootstrapping
• [ ] example plot should include bootstrapping

[joshuawe]

Almost done. But first the new bootstrapping function should be included.