Added: New themeable component, Chat Header - customize the chat header with the new HTML & CSS template.

Added: New themeable component, No Chats view - customize the messaging and layout of the view when there aren't any chats with the new HTML & CSS template.

Added: Autofocus the message field on desktop devices, new option to toggle this behaviour with messageField.autofocus.

Fixed: When a user has been removed from a conversation, it will no longer be reported as unread when new messages come in.