Add prod/dev modes for eslint config

Created by: alexkrolick

Adds a strict "prod" option to the ESLint config to address some of the concerns about looseness when using the config outside create-react-app

package.json

{
    "eslintConfig": {
        "extends": ["react-app/prod"]
    }
}

• react-app/dev - same as current config, mostly warnings
• react-app same as dev
• react-app/prod - escalates warnings to errors