Feature: Configurable subsidy duration

src/table/settings/settings.ini

@@ -231,6 +231,19 @@ str      = STR_CONFIG_SETTING_SUBSIDY_MULTIPLIER
 strhelp  = STR_CONFIG_SETTING_SUBSIDY_MULTIPLIER_HELPTEXT
 strval   = STR_SUBSIDY_X1_5
 
+[SDT_VAR]
+var      = difficulty.subsidy_duration
+type     = SLE_UINT16
+from     = SLV_CUSTOM_SUBSIDY_DURATION
+flags    = SF_GUI_0_IS_SPECIAL
+def      = 1
+min      = 0
+max      = 5000
+interval = 1
+str      = STR_CONFIG_SETTING_SUBSIDY_DURATION
+strhelp  = STR_CONFIG_SETTING_SUBSIDY_DURATION_HELPTEXT
+strval   = STR_CONFIG_SETTING_SUBSIDY_DURATION_VALUE
+
 [SDT_VAR]
 var      = difficulty.construction_cost
 type     = SLE_UINT8