Add the ability to export charts from Chart Widget in AWAB/AGOL

[DanielGetz]

In this example, the chart widget is being used to measure the change in elevation across contours. The output of the profile graph created by the widget is shown here. The only way to share the graph with others is to screenshot the chart itself, and the output of the graph when screenshot is a little confusing without the option to add your own legends.

This widget would be greatly improved by the ability to add a custom legend name for each axis and the ability to export the resulting chart/charts.