private void AddCommand_Execute()
 {
     Uri destination = NavigationMap.ResolveDestination(NavigationDestination.ClientAddEdit);
     NavigationMessage message = new NavigationMessage() {NavigateTo = destination};
     Messenger.Default.Send(message);
 }
 private void EditCommand_Execute()
 {
     Uri destination = NavigationMap.ResolveDestination(NavigationDestination.ClientAddEdit, SelectedClient.Id.ToString());
     NavigationMessage message = new NavigationMessage() { NavigateTo = destination };
     Messenger.Default.Send(message);
 }