Refactored on_ok method in MessagingHelper.
Added log.fatal when message_queue is empty in response handler for every response originated from a request (e.g. :order_change and :order_completed are standalone responses). Also I've cleaned few on_* methods.
Added custom_deserializer for order_type which deserializes order_type as symbol.
Moved code responsible for moving resources on order acceptance from on_ok to on_order_accepted - it was an obvious bug.
Cleaned methods on_list_of_stocks and on_list_of_orders.