The old model of coin movements attempted to compute fees etc and log
amounts, not utxos. This is not as robust, as multi-party opens and dual
funded channels make it hard to account for fees etc correctly.
Instead, we move towards a 'utxo' view of the onchain events. Every
event is either the creation or 'destruction' of a utxo. For cases where
the value of the utxo is not (fully) debited/credited to our account, we
also record the output_value. E.g. channel closings spend a utxo who's
entire value we may not own.
Since we're now tracking UTXOs onchain, we can now do more complex
assertions about the onchain footprint of them. The integration tests
have been updated to now use more 'chain aware' assertions about the
ending state.
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.
