Updating requirements/environment

[Will-Cooper]

closes #141, simplify requirements.txt and environment.yml, swap mult…multiprocessing for multiprocess to work on Mac.
Can test with:

conda env create --name simpletest -f environment.yml
conda activate simpletest
python -m simple_app.app_simple
conda deactivate
conda env remove -n simpletest

[dr-rodriguez]

I like the simplification, but we should considering pinning the requirement versions, especially since this is the website. The general user can grab the latest, but the website should have pinned versions or an update can break it.

[Will-Cooper]

I agree, I'm also considering upgrading the python version on the website to get ahead of the game. Just need to do some fixes as there's several changes in pandas etc.