add "out of visible range" arrow for box plots

[gvwilson]

We would like to request an option to enable "out of visible range" arrows for boxplots. See below screenshot for an example:

The intention is to show the reader that the range was intentionally chosen to focus on the middle quartiles, as the max and min values are far out.

It would also be interesting to see this for scatter plots, but this a second priority.

[gvwilson]

Oh that's an interesting idea - so whenever the upper or lower fence is outside the viewport, put a small arrowhead at the edge of the viewport.

My gut reaction is to make an attribute like:

overflowmarker: {
    size: 10
}

which would enable this and give it a ~10px width (similar to how scatter markers are sized) but would also allow us to modify it further in the future by adding other attributes in the same container.