Commodity(commodityCode: String, displayName: String, defaultFractionDigits: Int = 0)
Class representing a commodity, as an equivalent to the Currency class. This exists purely to enable the CommodityContract contract, and is likely to change in future.
commodityCode - a unique code for the commodity. No specific registry for these is currently defined, although
this is likely to change in future.
displayName - human readable name for the commodity.
defaultFractionDigits - the number of digits normally after the decimal point when referring to quantities of
this commodity.