console: aggregate metrics from the datastream

[hawkw]

it would be cool if the console could also aggregate metrics from the incoming data and compute percentiles of stats like scheduler latency, active tasks, and poll/idle durations over a rolling time window. we could display histograms or sparklines in the UI, as well as just displaying numeric values; tui has sparklines, bar charts and line charts that might be useful...

[bIgBV]

I like the idea of using sparklines to show this information. Something that would be really cool would be to provide a perf report like UI where you can dig into hot spots to narrow down which task is causing a particular parent task to slow down. And would we want the time window to be dynamically configurable?