Intelligent chart layouts

[tawheeler]

This long-term feature request would figure out an intelligent way to arrange the charts on the canvas to make best use of the space available. Perhaps grow and shrink them as needed.

[tawheeler]

Note: we can control the size of the charts and the size of the iframe, so this should be possible. Perhaps we want to move away from float::left?

[tawheeler]

I started to address this with commit d161800. We can be cleaner about how we set the iframe width, row height, and how we lay everything out in general. The commit does size the iframe nicely though to avoid scroll bars.