Add multilingual functionality to the site

[JonathanReeve]

This adds i18n functionality to the site, allowing the user to switch between languages. I google-translated the site content in some places to start it off.

I also changed the default language away from English. The way I see it, if DH is too English-centric, why not set a good example by avoiding anglocentrism on the website, too? I changed it to Esperanto, the most commonly spoken neutral language, so as to avoid implicitly privileging any particular national language. This is an unusual choice, but I think you'll agree that it's a bold statement that critiques the dominance of the English language on the Internet.

The theme has some changes, because the Jekyll theme that was there previously didn't play nicely with this setup. But that's a good thing, since the codebase is now much smaller, and the site is much more maintainable. This is easy to change, though—for instance, with a drop-in CSS framework like Bulma. Or better yet, just by adding a couple of lines of style to the SASS.

Let me know what you think! You can preview this PR at https://jonathanreeve.github.io/multilingual-dh.github.io/.

[quinnanya]

Thank you so much for doing all this! It's been a huge roadblock. I was going to try to sort it out with Alex Gil next week, but it's amazing to have help with it.

[JonathanReeve]

Happy to help! Thanks for merging.

[shuiowa]

Hello, I may contribute a Chinese edition to the "manifesto", if you don't mind.

[quinnanya]

That would be wonderful, thank you! Would it work for you to submit a pull request with the changes?