Better data viz for throughput

Throughput is the number of people crossing a road or intersection over time. Check out `TimeSeriesCount` in `sim/src/analytics.rs`.

The `raw` data is too big to store for most scenarios, so there's very basic compression into per-hour X mode counts. But the way that's later plotted in the live line plots (info panels for lanes and intersections) looks strange, because as the live sim progresses, the bucket for that hour fills up until it reaches the typical value at the end. It'd be better to store the more accurate shape of the throughput-over-time graph and make comparisons with that. I've tried using the `lttb` crate to do this, but the compressed shape only resembles the baseline by the end of the day.

That explanation was probably kind of nonsense, sorry. Basically, if you're interested in data viz, jump on this bug and I'll explain more clearly. :)