public JobManager(ILoggerFactory loggerFactory)
{
logger = loggerFactory.CreateLogger <JobManager>();
logger.LogTrace("creating jobManager");
this.TotalProgress = new DerivedProgressionManager(Progress, loggerFactory);
this.StateChanges = Progress
.Connect()
.Transform(prog => prog.WhenAnyValue(vm => vm.State))
.ToCollection()
.Select(Observable.CombineLatest)
.Switch()
.Select(JobStateHelper.MergeStates);
}