[#421] Resolve "signalc: handle broken connection to signal server"

Closes #421 (closed)

Changes:

• Add in shutdown mode logic to determine when client is unsubscribing
• Resubscribe when server connection error encountered
• Change timer for read timeout to just under 1 minute (server has a 60 second idle timeout)
• Create SignalcCancellation.SubscriptionDisrupted error
• Add resubscribe counter

QA:

• To simulate IOException from server, put delayed execution block above read that shuts down the message pipe

launch {
  delay(15.seconds)
  messagePipe.shutdown()
}

• To simulate IOException from shutdown, send shutdown command to signalc
• To simulate TimeoutException, set readTimeout in config to something really short