Update the lightningd <-> channeld interface with lots of new commands to needed to facilitate spicing.
Implement the channeld splicing protocol leveraging the interactivetx protocol.
Implement lightningd’s channel_control to support channeld in its splicing efforts.
Changelog-Added: Added the features to enable splicing & resizing of active channels.
And no longer insist on opt_quiesce.
Changelog-EXPERIMENTAL: Config: `--experimental-upgrade-protocol` enables simple channel upgrades.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>