Definitely not as nice as it could be, but it works for now. This is
primarily intended as a simple dump method that just saves everything
to the database. We will later use smaller incremental updates to
update specific things. wallet_channel_save serves both to insert as
well as update.
This needed a rather annoying hack since sqlite3 can only store
integers up to 2^63, so I just squash it down/invert it, and hope that
we never ever have more than 2^63 updates.
Splitting the detection for outputs that we own into a separate
`wallet_extract_owned_outputs` function and use it when the broadcast
succeeds to re-add the change output back to the database.
Wallet should really be the container for anything bip32 related, so
I'd like to slowly wean off of `ld->bip32_base` in favor of
`ld->wallet->bip32_base`
We'll re-use them a few times so having them at a central location is
nice. We also fix a bug that was unreserving UTXO entries upon free,
instead of promoting them to being spent.
Since we have a simple way to query the database for UTXOs we can
simplify some of the coin selection logic. That gets rid of the
in-memory list of UTXOs.
