private void MenuItem_Clicked(object sender, EventArgs e)
        {
            // edit
            EditMachinePage page = new EditMachinePage(ref machines, (int)(sender as MenuItem).CommandParameter);

            Navigation.PushAsync(page);
        }
        private void ToolbarItem_Clicked(object sender, EventArgs e)
        {
            //add machine
            Machine machine = new Machine {
                Name = "", IPString = "", ID = machines.Count
            };

            machines.Add(machine);
            EditMachinePage page = new EditMachinePage(ref machines, machine.ID);

            Navigation.PushAsync(page);
        }