message: Add new config parameter for connection timeouts
  In order to remove frozen BASP nodes in a timely manner, users need to
  be able to provide a timeout on the messaging level. Ideally, this
  timeout is a multiple of the heartbeat interval.
diff: @@ -184,6 +184,9 @@ void middleman::add_module_options(actor_system_config& cfg) {
  .add<size_t>("max-consecutive-reads",
  "max. number of consecutive reads per broker")
  .add<timespan>("heartbeat-interval", "interval of heartbeat messages")
  + .add<timespan>("connection-timeout",
  + "max. time between messages before declaring a node dead "
  + "(ignored if heartbeats are disabled)")
  .add<bool>("attach-utility-actors",
  "schedule utility actors instead of dedicating threads")
  .add<bool>("manual-multiplexing",
  