Added multislot logic for cars

- "correctly" handling multiple ammo slots (three solutions)
- not scanning surfaces twice anymore

settings.lua

@@ -13,6 +13,13 @@ data:extend({
         name = "gun-turret-alerts-car-enabled",
         setting_type = "runtime-per-user",
         default_value = true
+    },
+    {
+        type = "string-setting",
+        name = "gun-turret-alerts-mode",
+        setting_type = "runtime-per-user",
+        allowed_values = {"added","individually","selected"},
+        default_value = "selected"
     },
 	{
         type = "int-setting",
@@ -20,7 +27,5 @@ data:extend({
         setting_type = "runtime-per-user",
         default_value = 8,
 		minimum_value = 0
-		
-    }
-	
+    },
 })