Better visibility into connectivity status

[jvperrin]

Currently it's hard to tell if messages are getting through from IRC -> Slack or Slack -> IRC unless you are on both at once and see the messages go through or check on the IRC logs. It would be nice to have some indicator that messages have gone through, or (more helpfully), an indicator when they haven't gone through successfully. This sorta works currently, since the irc-bridge user on Slack will have a green "online" indicator when it is connected successfully, so you can tell when messages from Slack won't go through to IRC, but for messages going from IRC -> Slack, it is not clear at all apart from seeing which messages get mirrored to Freenode successfully.