Accessibility

Features

• Accessibility (Only Available in React 16+). Frames now have tabindex on the viz groups (pieces and summaries in OrdinalFrame, nodes and edges in NetworkFrame, lines and areas and points in XYFrame) so you can tab to the viz group and then hit enter and arrow key through the individual items, which are described with aria labels and some rudimentary descriptions. Please let me know how I can improve it.

• Array position is available in tickFormat for axis elements as the second argument, so (d,i) => i would work for tickFormat.