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Modification for the Order, saves data that is set by Modifiers
e.g: shipping, tax, vouchers etc. Instead of linking to a Modifier it takes the Amount that the modifier will ammend the Order total by and the Description of the Modifier and saves that - denormalising the data - so that Modifiers can be deleted without losing any information from the Order.
DB fields for the order Modification, the actual Modifier data is saved into this class so if a modifier is deleted the order still has the necessary details.