Add dashboard plot to stream events

We have an event stream currently. It's not great. I suggest a compound chart with two parts:

1. A chart with one row per event type (other than worker addresses) with a dot placed for each event. This should give an idea for the frequency of different kinds of events. This will have to stream as events come in.
2. Below that, a table view that includes the content of the messages of one event type. We can toggle this by clicking on any of the rows of the chart above. As we click on a row we see the most recent ~20 or so events of that type streaming through.

We will also want a pause button that disconnects the stream, so that people can see and inspect what happened