Refactoring: split up "Variations" page

[markerikson]

This is the page in the repo I care about the least, and it's also gotten huge. It's where I dump anything that looks like it might be useful to someone, but that I think goes against the intended spirit / usage of Redux.

Right now there's only one category header within the page, and that's the "Redux-Inspired Libraries" section I just added today at the bottom. However, I've seen several groups of libs show up in that list:

• Abstractions over connect
• Class-based action creators and reducers
• Higher-level abstractions like Kea and Dva

And probably some more I'm not thinking of now.

So, while this page is the lowest priority for refactoring, it'd be nice to have it cleaned up at some point.