Merge pull request #3129 from optout21/splicing-msgs-update

Update splice messages according to new spec draft

diff --cc lightning/src/events/mod.rs
Simple merge

diff --cc lightning/src/ln/channel.rs
Simple merge

diff --cc lightning/src/ln/channelmanager.rs
Simple merge

diff --cc lightning/src/ln/functional_test_utils.rs
Simple merge

diff --cc lightning/src/ln/interactivetxs.rs
Simple merge

diff --cc lightning/src/ln/peer_handler.rs
Simple merge

diff --cc lightning/src/util/test_utils.rs
Simple merge