Cleanup the card implementation, add some readme files and update namespaces

Assets/Scripts/UI/CardSystem/CardUIElement.cs

@@ -1,15 +1,12 @@
 using System;
-using System.Collections.Generic;
 using AppleHills.Data.CardSystem;
 using Core;
-using UnityEngine;
 using TMPro;
-using UnityEngine.UI;
-#if UNITY_EDITOR
 using UnityEditor;
-#endif
+using UnityEngine;
+using UnityEngine.UI;
 
-namespace AppleHills.UI.CardSystem
+namespace UI.CardSystem
 {
     /// <summary>
     /// Handles displaying and interacting with a single card in the UI.