Better handling when loosing connection with broker

[Former user]

Currently, when there is no connection with the broker (because the broker is down, restarted or there is no network), message manager will try to enumerate queues/brokers and hangs. Message Manager can only be killed with the task manager and started again.

Tested this with latest ActiveMQ version on Windows with a shutdown/restart. The wished behavior is that message manager (without popups) show that the connection is lost and reconnects for x period of time (maybe changed in the settings).