Let TMDNibController itself manage live controllers
Dispose nib controller if no client is waiting when window closes

I don’t think there is any valid use-case where we are not using --wait, but still want to keep the nib around after the window is closed, as there is no bindable property for NSWindow that controls whether or not the window is open, so no way to re-open it.
Add newline to error strings (nib command)

Also include the token/nib name in the error string.
Update nib command’s help text to mention auto-dispose feature