Add settings for town/industry cargo production scaling modes

src/economy_type.h

@@ -253,6 +253,13 @@ enum TickRateMode : byte {
 	TRM_END,             ///< Used for iterations and limit testing
 };
 
+enum CargoScalingMode : byte {
+	CSM_BEGIN = 0,         ///< Used for iterations and limit testing
+	CSM_MONTHLY = 0,       ///< Traditional cargo scaling
+	CSM_DAYLENGTH,         ///< Also scale by day length
+	CSM_END,               ///< Used for iterations and limit testing
+};
+
 struct CargoScaler {
 private:
 	uint32_t scale16 = 1 << 16;