Set up Heroku deploys

[stevenbuccini]

This PR does several things to enable automatic deploys to Heroku from GitHub merges.

Description

This PR does several things:

• Adds a Procfile to tell Heroku how to run our app
• Adds a build task to the root package.json, which Heroku automatically looks for in its build step
• Removes the unzip package (which is deprecated) and replaces it with unzipper which is a drop-in replacement. The outdated unzip package was causing failures in our ETL process.
• Updates documentation.
• Updates the production configuration in the Express server to properly serve our static frontend.

Related Issue

Resolves #165

Motivation and Context

So others can use all of our hard work!

How Has This Been Tested?

Deployed the code to Heroku and tested all flows.

Screenshots (if appropriate):

N/A, you can see it live here!

Checklist:

• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.