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

Models/Company.cs

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+using System;
+
+namespace Invoice_App.Models;
+
+public class Company
+{
+    public string CompanyName { get; set; }
+    public string? LogoPath { get; set; }
+    public string Address { get; set; }
+    public string ZipCode { get; set; }
+    public string City { get; set; }
+    public string CVR { get; set; }
+    public string PhoneNumber { get; set; }
+    public string? AccountRegistration { get; set; }
+    public string? AccountNumber { get; set; }
+    
+}

Models/Customer.cs

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+namespace Invoice_App.Models;
+
+public class Customer
+{
+    public string Name { get; set; }
+    public string Address { get; set; }
+    public string? ZipCode { get; set; }
+    public string? City { get; set; }
+    public string? PhoneNumber { get; set; }
+    public string? Email { get; set; }
+}

Models/Vehicle.cs

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+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; }
+}