Add jekyll-simple-i18n plugin with example

Adds in support for https://github.com/signalapp/jekyll-simple-i18n.

The plugin did not work with the github-pages gem, so github-pages was
switched with jekyll (which is what the current i18n branch does anyway).

_data/language_map.yml

@@ -0,0 +1,47 @@
+---
+af: "Afrikaans"
+az: "Azərbaycanca"
+bg: "Български"
+ca: "Català"
+cs: "Česky"
+da: "Dansk"
+de: "Deutsch"
+el: "Ελληνικά"
+en: "English"
+es: "Español"
+et: "esti"
+fa: "فارسی"
+fi: "suomi"
+fil: "Pilipino"
+fr: "Français"
+ga: "Gaeilge"
+hr: "Hrvatski"
+hu: "Magyar"
+id: "Bahasa Indonesia"
+it: "Italiano"
+ja: "日本語"
+kk: "Қазақ"
+ko: "한국어"
+lt: "Lietuviškai"
+lv: "Latviešu"
+mk: "Македонски"
+ms: "Bahasa Melayu"
+nb: "Norsk"
+nl: "Nederlands"
+pl: "Polski"
+pt_BR: "Português (br)"
+pt_PT: "Português (pt)"
+ro: "Română"
+ru: "Pусский"
+sk: "Slovenčina"
+sl: "Slovenščina"
+sr: "српски"
+sv: "svensk"
+sw: "Kiswahili"
+th: "ภาษาไทย"
+tr: "Türkçe"
+uk: "Українська"
+uz: "O'zbekcha"
+vi: "Tiếng Việt"
+zh_CN: "简体中文"
+zh_TW: "繁體中文"