Clipboard action now sets an expiration timer

WIP Max History count (back-end done, front-end todo)

ModernKeePass.Application/Database/Models/DatabaseVm.cs

@@ -12,5 +12,6 @@
         public string KeyDerivationId { get; set; }
         public int Size { get; internal set; }
         public bool IsDirty { get; internal set; }
+        public int MaxHistoryCount { get; set; }
     }
 }