higher-level zoom features

[gordonwoodhull]

Splitting a bullet from #100 "pan/resize/zoom defaults" into its own issue.

It seems like zoom is more complicated than just one set "strategy" - you want one behavior for the first display, which is usually but not always the render (sigh), and even after that it may be a little more complicated.

fitStrategy 'zoom' is a stupid name; it should be bring-in-bounds or something.

What's usually wanted is

• fit once, stretching the least of vertical or horizontal ('default')
• but if that's more than the max zoom, align top left or optionally center
• after that, respect the user's zoom except bring things in bounds, and also bring things in bounds when the layout changes
• alternately, the client may want to zoom to fit on any change to the data, but that's kind of disruptive (unless mouse zooming is entirely disabled?)

[gordonwoodhull]

We can keep it all configurable like it is now, but there are probably only 2-3 cases which almost everyone will want. E.g. maybe it's just "zoom once and then leave it to the user but bring things in bounds" or "always zoom and don't give the user any control"

[gordonwoodhull]

Render should cause "zoom once", and the client should be able to invoke "zoom once" for the next redraw when some action occurs, like a change of filters.