[Move contour plots to Python from LaTeX -- Faster compile]

[nipunbatra]

• [ ] Replace all tikz figures in https://github.com/nipunbatra/ml-teaching/blob/master/ml-maths/ml-maths-2-contour.tex with Python generated figures from https://github.com/nipunbatra/ml-teaching/blob/master/notebooks/contour.ipynb
• [ ] Move the ml-maths-2-contour.tex to slides/ folder
• [ ] Clean up (remove all the temp files like the following)