eth-watcher: store logs in state to implement peer
eth-watcher: store logs in state to implement peer

In order to give an initial response to incoming subscriptions (without
resorting to retrieving that data from chain again) we now store event
log history in state.

Instead of discarding pending-logs entirely after sending out updates,
we add them to the watchdog's history.
Just like pending-logs, we remove from the head during a rewind (though
not before exhausting the pending-logs).

jfranklin9000/urbit,jfranklin9000/urbit,ngzax/urbit,jfranklin9000/urbit,urbit/urbit,ngzax/urbit,ngzax/urbit,ngzax/urbit,ngzax/urbit,jfranklin9000/urbit,jfranklin9000/urbit,ngzax/urbit,urbit/urbit,jfranklin9000/urbit,urbit/urbit,ngzax/urbit,urbit/urbit,jfranklin9000/urbit,urbit/urbit,urbit/urbit,urbit/urbit