Add layering plots to example gallery (#2560)
Add layering plots to example gallery (#2560)


vega/vega-lite,vega/vega-lite,vega/vega-lite,uwdata/vega-lite,vega/vega-lite,uwdata/vega-lite,uwdata/vega-lite,vega/vega-lite,uwdata/vega-lite,uwdata/vega-lite