optimize Order class so that it uses less RAM

[ArjunVachhani]

• OrderCondition property only required when order is entered into the system. so while adding order by calling AddOrder method if it is passed, then it does not need to required for the rest of the life of order object.

• IsTip property is just a flag, it represents that the order is a tip of the iceberg order or not. We can have a Tip class that is inheriting Order. instead of order.IsTip can check with order is Tip