Some major changes (#3388)

* Some major changes

I streamlined this to just one option: CSS Modules. I saved all the text that I took out in case we need it later or want to put it back in. 

One edit that I wrote in my notebook, which I now don't understand, reads: "Tell people to create `src/pages/about-styled-components.js`

* Update index.md

* Reintroducing Glamor and Styled Components as "bonus" items

Now they are separate mini-tutorials.

* Update index.md

* Update index.md