Changes way viruses are stored in mobs.

Now it's an associative list:
uniqueID - virus datum

Updated most instances to match it.

code/modules/reagents/Chemistry-Reagents.dm

@@ -930,8 +930,9 @@ datum
 				// radium may increase your chances to cure a disease
 				if(istype(M,/mob/living/carbon)) // make sure to only use it on carbon mobs
 					var/mob/living/carbon/C = M
-					if(C.virus2)
-						for (var/datum/disease2/disease/V in C.virus2)
+					if(C.virus2.len)
+						for (var/ID in C.virus2)
+							var/datum/disease2/disease/V = C.virus2[ID]
 							if(prob(5))
 								if(prob(50))
 									M.radiation += 50 // curing it that way may kill you instead