New static repr of matplotlib plots saved at low-res

[jklymak]

Describe the issue

#343 introduced static representation of matplotlib plots, which works great. Except the png is low res, whereas it would probably be nicer at highres, at least for those with hiDPI screens:

while widget Active

static repr of plot:

Versions

...master

[ianhi]

Removed code is here: #343 (comment) I think restoring that will go a long way.