Auto separation: Add setting to scale vehicle lateness adjustments.

No longer set vehicle lateness to 0 if separation fails, instead
leave it as it was.

The setting defaults to 100% (full abruptness, old behaviour).
Reduce the setting if auto separation is too disruptive, e.g. causes
excessive waiting in stations.

Note that this is not savegame compatible.

src/table/settings.ini

@@ -347,6 +347,20 @@ str      = STR_CONFIG_SETTING_TIMETABLE_SEPARATION
 strhelp  = STR_CONFIG_SETTING_TIMETABLE_SEPARATION_HELPTEXT
 cat      = SC_EXPERT
 
+[SDT_VAR]
+base     = GameSettings
+var      = order.timetable_separation_rate
+type     = SLE_UINT8
+from     = TIMESEP_SV
+def      = 100
+min      = 0
+max      = 100
+interval = 10
+str      = STR_CONFIG_SETTING_TIMETABLE_SEPARATION_RATE
+strhelp  = STR_CONFIG_SETTING_TIMETABLE_SEPARATION_RATE_HELPTEXT
+strval   = STR_CONFIG_SETTING_PERCENTAGE
+cat      = SC_EXPERT
+
 ; There are only 21 predefined town_name values (0-20), but you can have more with newgrf action F so allow
 ; these bigger values (21-255). Invalid values will fallback to english on use and (undefined string) in GUI.
 [SDT_OMANY]