Remove nix in favour of venv

[stickyPiston]

Currently, we use nix to manage python packages, but a more standard approach supported better by IDEs is to use python virtual environments. In my opinion, nix adds quite a bit of complexity (and flexibility) that we don't really need in the mongoose. Therefore I'd like to propose to use a less flexible but more simple tool for managing python packages: virtual environments.

[SilasPeters]

I agree. We should use venv and potentially virtualenv. Nix is great, but too complicated for this

[SamStaijen]

I think nix is great, but the learning curve looks too much like ln(x) in my opinion. I would prefer something like venv as well.

I also volunteer as a tester, if you are able to find someone to implement it that is :).

tl;dr: I Agree!

[stickyPiston]

Sweet, then I have a PR that implements a venv: #63. The installation instructions are quite a bit longer now, because the developer is responsible for installing the correct version of python.