Add item spawn menu

Fix game over bug
Start adding more implementation for jewels

Zennysoft.Game.Ma.Implementation/Game/GameRepo.cs

@@ -110,14 +110,14 @@ public class GameRepo : IGameRepo
   {
     AnnounceMessageInInventory("Experience points temporarily doubled.");
     DoubleExpTimeStart?.Invoke(lengthOfEffect.Seconds);
-    ExpRate = 2;
+    ExpRate *= 2;
   }
 
   public void EndDoubleExp()
   {
     AnnounceMessageOnMainScreen("Experience points effect wore off.");
     DoubleExpTimeEnd?.Invoke();
-    ExpRate = 1;
+    ExpRate /= 2;
   }
 
   public void AnnounceMessageOnMainScreen(string message)