Add fuel type dropdown and diesel fuel type.

Models/Vehicle.cs

@@ -13,6 +13,7 @@
         public decimal PurchasePrice { get; set; }
         public decimal SoldPrice { get; set; }
         public bool IsElectric { get; set; } = false;
+        public bool IsDiesel { get; set; } = false;
         public bool UseHours { get; set; } = false;
         public List<ExtraField> ExtraFields { get; set; } = new List<ExtraField>();
         public List<string> Tags { get; set; } = new List<string>();