Resolve package dependencies for installation

[agitter]

Requiring sklearn in setup.py installs the wrong package. The other changes make requirements.txt more consistent with setup.py.

I found it tricky to install this package from requirements.txt and created a compatible conda environment. I have that on a separate branch and could merge it here if you are interested.

[agitter]

I expanded the scope of this pull request to fix an error I encountered when trying to run the OmicsIntegrator command:

$ OmicsIntegrator
Traceback (most recent call last):
  File "/ua/gitter/miniconda3/envs/oi2/bin/OmicsIntegrator", line 5, in <module>
    from src.__main__ import main
ModuleNotFoundError: No module named 'src'

The edit in 7356b08 fixed this on my system.

[agitter]

I have a fork that fixes several of the command line-related issues I reported recently and adds basic GitHub Actions testing. I can expand the scope of this pull request to include those updates if you would like them here.

My goal is to prepare an Omics Integrator 2 Docker image that would simplify some of our command line use cases.