Refactor, cleanup code and add documentaiton

Assets/Scripts/CardSystem/StateMachine/ICardClickHandler.cs

@@ -0,0 +1,11 @@
+namespace UI.CardSystem.StateMachine
+{
+    /// <summary>
+    /// Implement on a state component to receive routed click events
+    /// from CardContext/CardDisplay.
+    /// </summary>
+    public interface ICardClickHandler
+    {
+        void OnCardClicked(CardContext context);
+    }
+}