public ActionResult Create(Activity activity)
        {
            if (ModelState.IsValid)
            {
                activity.Event = db.Events.Find(eventID);
                db.Activities.Add(activity);
                db.SaveChanges();
                return PartialView("GridData", new Activity[] { activity });
            }

            return PartialView("Edit", activity);
        }
        public ActionResult Edit(Activity activity)
        {
            if (ModelState.IsValid)
            {
                db.Entry(activity).State = EntityState.Modified;
                db.SaveChanges();
                return PartialView("GridData", new Activity[] { activity });
            }

            return PartialView(activity);
        }