Default to SVG output in VSCode & Atom

[jebej]

Currently, svg output is disabled by default because it is really slow in IJulia, something I have tested for myself. However, displaying svgs in e.g. VSCode works well, and gives the user sharper plots as a result.

Could we switch the default in this package to display svg, and either have IJulia itself disable the svg output, or PyPlot detect that it is running within an IJulia kernel?

[jebej]

I see that 3 environment variables are defined within a notebook served by the python notebook server. Maybe we can check for their existence.

"JPY_INTERRUPT_EVENT" => "1444"
"IPY_INTERRUPT_EVENT" => "1444"
"JPY_PARENT_PID" => "1456"