[general need] V2 Codes Cleanup

[servoz]

We have started to comment on them (by chance from working on something else 794fe57) but they should be deleted properly. It's not a priority, but it should be done one of these days!

[servoz]

I will start working on this ticket. I think the purpose of this one goes far beyond removing the parts that are no longer used in V2. I'm changing the title of this ticket right away to the more general title "V2 Code Cleanup".

I think the goals of this ticket are:

• Remove the parts of code that are not used anymore.
• Remove commented code parts, when it is clearly not a comment that can be used in a future planned modification.
• Add missing docstrings (functions, methods, classes, modules). For class, indicate the methods present in the class and their signature. For modules, indicate the classes present. Arrange, when possible, in alphabetical order (it's very time consuming to do, but let's not forget that our codes are first made to be read...)
• Respect the code writing standards (especially pep 8).

Let me know if I forget something.

[servoz]

After a big effort, I think we can now close this ticket, the cleanup is now done, as far as possible ...

Special attention has been paid to the docstring. Most of it is up to date. I admit I put ""Blabla"" a few times by laziness or lack of time... We can always do a search on Blabla and fix it later, when we have some time...

All UTs work correctly now and the codes match them with a minimum of exceptions (for example, for Flake8, only C901 and W503 which are almost impossible to meet).

There is only one issue with isort that I could not fix. One can, while waiting to solve this problem, live with it by running isort locally and commenting in .pre-commit-config.yaml file before pushing to GitHub.