TP 1 : Surviving in a flat world

[pomerlef]

In percep3d_students/exercises/assignement_2d/4-assignment_flat_world.ipynb

There are typos in the function `helper_func.py, the letter 's' is missing in:

• rigid_tranformation()

• scale_tranformation()

• [x] rename the functions

• [x] refactor the code to avoid errors

This was well spotted by a student of Summer 2022.

[WilliamDubois]

Corrections have been made in the exercises and lessons.