Aurora IRC Client localization layout

v0.8.3 establishes localization infrastructure without claiming an incomplete
translation as finished.

Localized User Guides:
  docs/i18n/<language-code>/USER_GUIDE.md
  docs/i18n/<language-code>/USER_GUIDE.html

English is the fallback. Icelandic uses ISO language code "is".
Future translated UI strings are catalogued separately from IRC/network logic.
