## What changes were proposed in this pull request?

Add metric on number of running tasks to status bar on Jobs / Active Jobs.

## How was this patch tested?

Run a long running (1 minute) query in spark-shell and use localhost:4040 web UI to observe progress.  See jira for screen snapshot.

Author: Eric Vandenberg <ericvandenberg@fb.com>

Closes #18369 from ericvandenbergfb/runningTasks.