Reorganise "Modules and Packages" and "Manage Python project"

[yakutovicha]

[edoardob90]

Partially related to #205

[despadam]

Hi @yakutovicha 👋

I went through the Modules and Packages notebook and in the end I don't think it is too much for the beginner's course, considering it is the last chapter that we will cover. By then they should feel more comfortable with Python and a chapter like this should not scare them away. It is useful knowledge, so I suggest we keep the content as is and let them see how far they can get. Perhaps the last part about GitHub will be a bit tricky if they haven't used it before, but I still think it's a good exercise.

My only suggestion would be to add a couple of extra sentences, explaining a bit better what a .toml file is, in the Make the package installable section.