Added classes for Company, Customer, and Vehicle. Also added test for Vehicle class

Models/Vehicle.cs

@@ -0,0 +1,13 @@
+using System;
+
+namespace Invoice_App.Models;
+
+public class Vehicle
+{
+	public string? Make { get; set; }
+	public string? Model { get; set; }
+	public DateTime? RegistrationDate { get; set; }
+	public string? VinNumber { get; set; }
+	public decimal? Kilometers { get; set; }
+	public string? Comments { get; set; }
+}