Allow an authentication-less setup

[Robert Klep]

I'd like to use MQTT Broker in combination with the MySensors app, so I don't have to run a separate MQTT broker somewhere else.

However, the MySensors app doesn't support authentication.

There's obviously a point to be made that this has to be fixed in MySensors and not in MQTT Broker, but I would still like to be given a choice if I want authentication enabled or not. I realise that this shouldn't be the default setting, but perhaps a checkbox ("allow unauthenticated connections") would be acceptable?

[scanno]

Added in the next version.