So while I quite like the legend at the top of the graph, the placement of the legend div causes two glitches now:

- as the legend grows, it seems that the graph chart isn't scaled down; instead, it keeps its current size and the entire chart area is just pushed out of the bottom of the frame, making the lower timeseries disappear

- hover-legends are no longer vertically aligned with their timeseries as these get pushed down by the legend

I'm still cool with the legend being either at the top or in a separate area at the bottom, depending on what is easier to accomplish.

I wonder if it would be possible to get the height of the legend before we render the graph, and calculate the graph height from that? The problem is that we 1) first construct the graph (where you'd normally pass in the height), 2) then create the legend, whose size we'd need for step 1. But maybe there's a way to change the graph height after construction, but before rendering. I'll look around a bit...