Add save graph as PNG to GRNsight

[mihirsamdarshi]

Added solution for #59 to GRNsight. @dondi wanted to see if it was ok to use this library and if the implementation was ok.

[dondi]

The code itself looks OK, but when I tested this locally, clicking on “Save Graph as PNG” produced two downloads of what appear to be the same image file. I also got some warnings that appear to be emanating from the saveSvgAsPng library (screenshot provided, showing both the double download and the warnings).

@mihirsamdarshi Please confirm whether you are seeing these two issues also, or if these might be isolated to my setup.

Also, from a design perspective, the “Save Graph as PNG” menu item strikes me as another “Export Data” choice, and thus best belongs within the “Export Data” submenu rather than as the last entry of the File menu.

Otherwise, things look good, but let’s try to clean up/investigate the above observations. Thanks!

[dondi]

I've gone ahead and merged this into beta so it can be tried out on the next release. However the comments from the review still stand and ideally they should be addressed before we release as final.

I can move the menu item to “Export Data” pretty easily, but the other changes will take deeper investigation (and confirmation first to see if it happens on other setups).