Remove gunicorn

We don't use it, we don't want it, We get rid of it.
Style, remove rhel
Style.
style. Enable installtion of single package into venv

* Make it possible to install a single package (+ deps) int venv
* By default, we (also) use --system-site-packages now.
add our own modules
Document the changes that we've made
Reuse class python::virtualenv for this installation
install pip (again) with the -dev package