Add eslint back to project

Need to either get off of react-dates (which isn't compatible w/React 17 + 18) or wait until react-dates is compatible in order to get back to eslint. (Currently, we need to build the project with npm i --legacy-peer-deps, which causes issues with eslint due to multiple React versions -- I think. Possible there's some way to get eslint working with the current setup.)

See eslint files removed in https://github.com/codefordenver/Comrad/commit/8b1ea83d706db12b908ff44d8e722cd0134cb872