Allow knowing which jobs are running (and not just submitted/pending and paused)

It seems like we can pretty easily know by looking at the `job.next_run_time` whether a job is paused or not but it is really hard to know if a job is running or not (as far as a I can tell) since there is no apparent job state that is connected to a job saying the job is actively running (the event notification system is not reliable enough to do this, as it can be fired out of order).

So this is more of a feature request to have such a capability...

If more details are needed (or I can suggest some ideas on how to do it or maybe even a PR).