remove JobStatus, Task abstraction and 'control status' subcommand

Control status will be replaced by job-specific output at some point.

Task was not useful anymore with state machine, may reintroduce
something similar at a later point, but consider alternatives:

- opentracing.io
- embedding everything in ctx
	- activity stack would work easily
	- log entries via proxy logger.Logger object
- progress reporting should be in status reports of individial jobs

cmd/config_job_prometheus.go

@@ -70,8 +70,6 @@ func (j *PrometheusJob) JobStart(ctx context.Context) {
 	}
 
 	log := getLogger(ctx)
-	task := NewTask("main", j, log)
-	log = task.Log()
 
 	l, err := net.Listen("tcp", j.Listen)
 	if err != nil {
@@ -94,6 +92,3 @@ func (j *PrometheusJob) JobStart(ctx context.Context) {
 
 }
 
-func (*PrometheusJob) JobStatus(ctxt context.Context) (*JobStatus, error) {
-	return &JobStatus{}, nil
-}