Adds option to limit sling unhatched duration

code/controllers/configuration.dm

@@ -68,6 +68,7 @@
 	var/assistantratio = 2 //how many assistants to security members
 
 	var/traitor_objectives_amount = 2
+	var/shadowling_max_age = 1800
 
 	var/max_maint_drones = 5				//This many drones can spawn,
 	var/allow_drone_spawn = 1				//assuming the admin allow them to.
@@ -260,6 +261,9 @@
 				if("jobs_have_minimal_access")
 					config.jobs_have_minimal_access = 1
 
+				if("shadowling_max_age")
+					config.shadowling_max_age = text2num(value)
+
 				if("log_ooc")
 					config.log_ooc = 1