Add the possibility to export Diagram (png, svg)

[Gsyltc]

Hello,

It would be interesting to consider the possibility of exporting diagrams as images (example: PNG or SVG).

Thank you

[alexmojaki]

@paulfitz @dsagal @georgegevoian @berhalak who's watching this repo?

[dsagal]

It looks like plotly supports a "mode bar" that includes a button to export graph as PNG. It's turned off with displayModeBar: false setting presumably because the mode bar is usually not needed, and would be more of a distraction. Perhaps what we need then is an option to turn on the mode bar?