Allow to pause a scan


When a scan is in progress on busy drives or over low bandwidth connections, it often results in race conditions or temporary overload due to parallel access between TS and other applications. If none of them is able to pause it's access, you do have no chance to speed it up by manually resolving the overload than either waiting or killing one of the processes.
Would be good if we could pause the TS scan (not *stop* - would just produce *more* load, as scan has to be started again later ...!) until workload drops. Automatic throttling by decrement of used threads would not be enough - *I'm* master of my equipment, not an algorithm.