v2 channel open uses a different method to derive the channel_id, so now
we save it to the database so that we dont have to remember how to
derive it for each.
includes a migration for existing channels
This moves the notification for our coin spends from when it's
successfully submited to the mempool to when they're confirmed in a
block.
We also add an 'informational' notice tagged as `spend_track` which
can be used to track which transaction a wallet output was spent in.
Previously we were annotating every movement with the blockheight of
lightningd at notification time. Which is lossy in terms of info, and
won't be helpful for reorg reconciliation. Here we switch over to
logging chain moves iff they've been confirmed.
Next PR will fix this up for withdrawals, which are currently tagged
with a blockheight of zero, since we log on successful send.
onchaind is the only daemon that emits coin events, and those are all
onchain (ha!), so the only 'wire' facility we need for coin moves are
for the 'chain' type.
