FEATURE: Allow jobManager to be interrupted by system SIGINT

[fcool]

This is a first draft, to checkout if this is something you are even going to accept. (It is fully functionally though - but it needs to be documented - which I'd love to do, if you accept)

This change allows the JobWorker to be interrupted on the Command-Line by pressing CTRL+C or sending a SIGINT-Signal at a safe state (it will only be interrupted if the last job had been completed successfully or a timeout occured)

Additionally the JobManager provides a new Message queues might use to signal, they are now safe to interrupt (ideally before they go sleeping in their own "waiting for timeout" handling)