async void GroupTappedAsync(object sender, ItemTappedEventArgs e)
{
var item = e.Item as Group;
var editPage = new GroupPage(new GroupViewModel(item, true));
await Navigation.PushAsync(editPage);
}
async void ExistingParticipateTappedAsync(object sender, ItemTappedEventArgs e)
{
var item = e.Item as Group;
var editPage = new GroupPage(new GroupViewModel(item));
await Navigation.PushAsync(editPage);
}