Un-eject and use CSS module

[akx]

As discussed on https://stackoverflow.com/questions/64443626/react-babel-core-module-not-found ,

this PR

• un-ejects the app by reinstalling create-react-app
• fixes the babel-core import snafu
• renames Burger.css to Burger.module.css so CRA can use CSS modules there (see https://create-react-app.dev/docs/adding-a-css-modules-stylesheet/)

[akx]

It looks like you didn't much care about this.

[sachuverma]

I didn't wanted to merge it right now because I was following the udemy tutorial, If I would have merged it now then the file structure and others things might have changed and I might face some problems, so wanted to work on the same code base