Update express app

#### Complete initial express app

- update the base express app to create a server that listens on port 3000
- add `npm start` script for easy running
- update basic `package.json` `README` & standards
- change `public/stylesheets` to `public/css`

:zap: :full_moon_with_face: :zap: :octocat: :zap: :thumbsup: