add vegawidget to applications-documentation (#4514)
add vegawidget to applications-documentation (#4514)

* adds vegawidget to applications documentation

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