[ADDED] the inlog screen and a data singleton for the client

Client/Views/LoginScreen.xaml.cs

@@ -0,0 +1,40 @@
+using SharedClientServer;
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Data;
+using System.Windows.Documents;
+using System.Windows.Input;
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+using System.Windows.Shapes;
+
+namespace Client.Views
+{
+    /// <summary>
+    /// Interaction logic for LoginScreen.xaml
+    /// </summary>
+    public partial class LoginScreen : Window
+    {
+        ClientData data = ClientData.Instance;
+        public LoginScreen()
+        {
+            InitializeComponent();
+        }
+
+        private void Button_EnterUsername(object sender, RoutedEventArgs e)
+        {
+            User user = new User(usernameTextbox.Text, 0, false);
+            Client client = new Client();
+
+            data.User = user;
+            data.Client = client;
+
+            MainWindow startWindow = new MainWindow();
+            startWindow.Show();
+            this.Close();
+        }
+    }
+}