Added Exit button.

Assets/ExitAppButton.cs

@@ -0,0 +1,27 @@
+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+using UnityEngine.Events;
+using UnityEngine.UI;
+
+[RequireComponent(typeof(Button))]
+public class ExitAppButton : MonoBehaviour
+{
+
+    private Button button;
+    void Awake()
+    {
+        button = GetComponent<Button>();
+        button.onClick.AddListener(OnAppExitRequested);
+    }
+
+    private void OnAppExitRequested()
+    {
+        if (Application.isEditor)
+        {
+            UnityEditor.EditorApplication.isPlaying = false;
+        }
+        
+        Application.Quit();
+    }
+}

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