public async Task OnEditContact(ContactViewModel contact)
{
SelectedContact = contact;
await DependencyService.Get <INavigationService>()
.NavigateAsync(AppPages.Edit, contact);
}
private async Task OnShowContactDetails(ContactViewModel cvm)
{
SelectedContact = cvm;
await DependencyService.Get <INavigationService>()
.NavigateAsync(AppPages.Detail);
}