Major updates to the first part of the francophone presentation

[pedrohbraga]

Hi!

This pull request contains the translation of the changes I performed to the first part of the presentation. These changes are described in pull request #15.

In summary, these changes address important issues with linearity and clarity that had been already raised by presenters and participants in this workshop. Most changes happened between the beginning and the hierarchical clustering methods part.

This update introduces simple concepts of matrix algebra. The material progressively builds on matrices and association matrices to then integrate a few commonly used distance coefficients and data transformation practices before the discussion about hierarchical clustering methods.

There is now more written text, which will help guide both presenters and participants through the material.

I also added a new challenge, cleaned the presentation and added presenter notes.

I am tagging the current presenters for this workshop to allow them to decide whether they want to incorporate these changes prior to their presentation.

[katherinehebert]

Made the same minor changes to the first and second halves of this presentation to match the English version. The most notable change involves additions to the final challenge, which was lacking code solutions on the slides. This branch is ready to merge if/when convenient!