Implement option_upfront_shutdown_script user-side

Implement option_upfront_shutdown_script user-side

We use user config to decide to commit to closing script
in open_channel/accept_channel messages. We don't check
that other peer supporting the option as including
script without other peer public support is borne by
the protocol. If user opt-out, following protocol and
due to the fact we always signal, we provide a zero-length
script