Streamline dependency management

[NMertsch]

Currently, this project uses pipenv.

Maybe this is a personal skill issue, but at least half of the time I spent contributing to this project was spent fighting with pipenv. Other contributors also mentioned that pipenv is causing major trouble for them.

[egeakman]

Yep, I am one of those contributors. It makes the setup harder for me, and I manually install all the packages using my preferred env manager.

I think it would be better if we used plain pip-tools, or make this an installable package. Both of these let you install the deps to your preferred environment.

Big ➕1️⃣ from me to change pipenv to something else.