New feature: transport groups (#172)

https://thepit.ja-galaxy-forum.com/index.php?t=msg&goto=365395

Tactical/Item Types.h

@@ -1220,6 +1220,10 @@ typedef struct
 	BOOLEAN fProvidesRobotLaserBonus;
 	//shadooow: bitflag controlling what system needs to be in play for item to appear
 	UINT8	usLimitedToSystem;
+
+	// rftr: the progress bounds that allow a transport group to drop an item
+	INT8 iTransportGroupMinProgress;
+	INT8 iTransportGroupMaxProgress;
 } INVTYPE;