Keep the accounts as an 'append only' log, instead we move the marker
for the 'channel_open' forward when a 'channel_open' comes out.
We also neatly hide the 'channel_proposed' events in 'inspect' if
there's a 'channel_open' for that same event.
If you call inspect before the 'channel_open' is confirmed, you'll see
the tag as 'channel_proposed', afterwards it shows up as
'channel_open'. However the event log rolls forward -- listaccountevents
will show the correct history of the proposal then open confirming (plus
any routing that happened before the channel confirmed).
