This counts the number of "standalone" mailboxes we create, which
happens when a client does open() without first using a nameplate. The
current client doesn't do this, but future clients might.
This moves responsibility for the periodic prune-everything Timer up to
RelayServer too. That way we can be sure the stats are dumped
immediately after prune, and we can incorporate stats from Transit as
well.
The new approach runs every 10 minutes and keeps a
nameplate/mailbox/messages "channel" alive if the mailbox has been
updated within 11 minutes, or if there has been an attached listener
within that time.
Also remove the "nameplates.updated" column. Now we only track "updated"
timestamps on the "mailboxes" table, and a new mailbox will preserve any
attached nameplate.
Unless/until people start writing new applications (with different
app-ids), this code is unlikely to get used very much, and the code is
simpler without it.
With increased usage, I'm seeing a buildup of stale channels. Since the
channels aren't properly ephemeral yet (where they get closed as soon as
the last subscriber disconnects), clients which terminate without
calling close() tend to leave the channel lying around. We don't have
"persistent wormholes" yet, so channels should be much more ephemeral
than they currently are.
Pass in a handle and a pair of functions, rather than an object with two
well-known methods. This should make it easier to subscribe to multiple
channels in the future.
