FastMail changelog update

The following changes have been rolled out to production:

• The keyboard shortcuts for reply/reply all have been reverted to “R”
  and “A” respectively to match the shortcuts used by other services.
• Preference added to change the default reply behaviour from “Reply
  to all” to “Reply to sender” (the preference is on the Settings ->
  Preferences screen, at the bottom of the “Writing” section).