Update Modelling Tutorials to Use `tidymodels` Framework

[deblnia]

Not sure how you feel about this -- definitely a difficult change to make, presumes some stat background, and probably goes along the lines of updating to encompass more of dplyr 1.0 -- but I've found the pre-processing framework fairly lovely, the documentation is good, and there are a few nice tutorials out there.

Talk soon 😄

[bensoltoff]

Definitely in my thoughts (see #230). I'm trying to re-envision the whole stat learning module. It covers two days and I presume no prior math background, so I have to start from square one essentially. I got rid of cross-validation and tree-based models because most students didn't seem to really understand how they worked (so much copy and pasting from the lecture notes). But I really like the tidymodels interface and I think it will be very useful for modelers moving forward.

That said, I'm not entirely comfortable shifting to it entirely. I still think students need to understand how to call some of the core model functions like lm() and interact with those objects.

[deblnia]

Closing to avoid redundancy!