New guides for your account, friends, emails, modes and building on Elixir

Eight new pages in the docs, each about one thing you came to do: your account (signing in, your players, your time zone, removal), following a friend and watching any player, milestone emails, turning an email off, why modes are kept apart, signing in to Elixir's own apps with your Elixir account, and the JSON API. Three older pages pointed at the console's Overview for things that live on Tracking and Profile, and now point at the right place. No change to the tools.