Some improvements to OOB notebook

[mdbenito]

Description

This PR adds some text and supporting functions to the OOB notebook.

Changes

• Moves data prep to the supporting module
• Adds a method to draw confidence intervals (normal and t)
• Redoes a couple of plots using it
• Adds random seed handling to compute_data_oob
• Ensures reproducibility of the notebook by passing around the seed
• Does some minor renaming in oob.py

I also sneaked in a couple of unrelated things:

• An adjustment of font sizes in the api docs
• Minor cosmetic changes here and there

Checklist

• Wrote Unit tests (if necessary)
• Updated Documentation (if necessary)
• Updated Changelog
• If notebooks were added/changed, added boilerplate cells are tagged with "tags": ["hide"] or "tags": ["hide-input"]

[mdbenito]

@BastienZim I've worked a bit on your notebook, let me know if you have comments. I was a bit surprised by the very different results that one can obtain with different seeds, often obtaining a degradation of performance with the removal of the worst 20% points. In the end I added complete randomization of the whole run including the splitting of the dataset to see what the true variance is. It is a lot more, but things are predictable. I also added random seed handling to compute_oob and did a couple minor things here and there

[AnesBenmerzoug]

Looks good to me. It's only missing a changelog entry.