* Currently depends on the wallet, but that will change in the near
future due to new additions to btcwallet currently under review.
* Re-orgs aren’t intelligently handled yet. To be done along with tests
in a later commit.
* So far very simple, only notifications for tx confirmations, and
outpoint spends.
* Our two cases are: waiting for the funding transaction to reach a
depth of N confirmations, and open channels being notified of the
counterpart trying to cheat them by broadcasting an invalidated
commitment tx.
* Goal is to backend agnostic source to chain notifications
* Open channels will communicate with this source to register intent
for critical notifications
* Pending notifications will need to be committed to disk.
* Will also need a journal to ensure no notification is missed
* Later goals include extending this to communicate with 3rd party
outsource services
