Translate Who Goes First into multiple languages.

[tswast]

With #15 we'll have the first bit of translation done (translating text with Babel). We'll need a few more things before I can call translation "done" though.

• Translate URLs for cards.
• Translate "about us".
• Improve instructions for how to translate. (Is there an online tool to recommend?)
• Add hreflang tags to each page.

[tswast]

This PR adds a translated "about us" page: #19

[tswast]

hreflang tags were added in #17

[tswast]

I should make it so that each card has its own language list. That way I don't have to translate every card when adding a new language. Also then I won't have to translate new cards into all languages right away.

[tswast]

I'm thinking we should make it so that the URLs are translated in the same way as the rest of the text (and have the English URL redirect to the translated one once there is a translated one).