Move logx, logy, logc, color-autoscale buttons from toolbar to axes

[nvaytet]

The logx, logy, log and color-autoscale buttons in the toolbar are designed to act on one axes.
The Home, Pan, Zoom, and Save buttons act on all axes in a subplot.

It was ambiguous what to do with the toolbar buttons when subplots/user-supplied axes/tiled were used.

We now move them to being on the axes themselves, appearing upon hover.

1d plot:

2d plot:

3d plot:

Note: for 3d plots we replaced the ipywidgets.Image widget with a custom Anywidget because the former does not handle hover or click events.

[nvaytet]

The View is the one who knows how to properly autoscale the axes because it holds the references to the plotted artists. But the canvas need to call autoscale when the log buttons are clicked. So we pass the callback to the canvas here.

Not the most elegant design but it was the least invasive I could come up with.