Improve activation status to show the true state

Status leds and user infos of the RabbitMQ modules should reflect the true activation state. Currently users get a confirmation message and status leds turn green when a given page is handed over to RabbitMQ instead of when the page has successfully activated. This can confuse users a lot.

Also, please hide system error messages from users and replace them by easy to understand infos, e.g. when the RabbitMQ server is unavailable or when there's some other problem with activation.