What has the execution engine been up to?

[kbergin]

As a user maintaining an execution engine, I'd like to know what this execution engine has been running in the last X number of hours. Similar to the timing diagram that is at the task level in Cromwell, this could be a timing diagram at the workflow start->stop level, with all running workflows from that time period showing. This report could also show a user how long the submission of jobs they made has been taking and how many were running at any given time.