feat(difficulty): Add string for difficulty page

Adds a string token for the not-yet-implemented Difficulty page.
fix(i18n): typo and update locales
fix(quests): Temporarily remove "booted" text

Users are confused by the fact that dying doesn't actually eject them from their current quest, as advertised. This commit removes that text from the English locale; we can put it back when the feature is implemented.
Separate out index.coffee into smaller files.