Merge branch '37-in-classifiers-overview-fixes-and-updates-for-scikit-learn-developments' into 'master'

Resolve "In classifiers overview: fixes and updates for scikit-learn developments"

Closes #37

See merge request sis/courses/machinelearning-introduction-workshop!29

Merge branch '24-in-pipelines-mention-transformers-caching-to-avoid-duplicate-computations' into 'master'

Resolve "In pipelines: mention transformers caching to avoid duplicate computations"

Closes #24

See merge request sis/courses/machinelearning-introduction-workshop!28

In classifiers overview: improve test data points visibility, add mutli-level stacking image, fix typo and formatting (black)

In classifiers examplse extra notebook: remove deprecated n_jobs from KMeans, fix dataset path, add decision tree prunning, format (black)

In pipeplines and hyperparameter search: fixed transformers caching section, reconciliated with pickling, added both to final excercises

Minor improvements

See merge request sis/courses/machinelearning-introduction-workshop!17

Merge branch 'master' of https://sissource.ethz.ch/sis/courses/machinelearning-introduction-workshop

Merge branch 'master' of https://sissource.ethz.ch/sis/courses/machinelearning-introduction-workshop