Rework lectures ordering in linear models module

[glemaitre]

TODO:

• [x] switch from California housing to Ames housing in regularization lesson to check if the model polynomial + ridge cv is stable. Done in https://github.com/INRIA/scikit-learn-mooc/pull/698

New ordering

• Consolidate the "Intuitions on linear models" by adding:
  • The full content of "Linear regression"
  • The notebook and quizzes from "Linear Classification" (try to change the notebook to use the default value of C and penalty).
• Rename lesson "Modelling non-linear features-target relationships" to e.g. "Non-linear feature engineering for linear models"
• Move and rename "Beyond linear separation in classification" in this new lesson.
• Delete Exercice M4.04, this will "fix" #641 as a consequence
• Replace it by Exercice M4.05