feat: export of canvas based vis to png

Canvas based visualizations (nodelink, matrix, mapvis) are exported to PNG using the the same procedure: forwarding reference.

Visualization panel is modified to allow to do that from a common call, by adding a capture button. Included keyboard shortcut (useful for interactions). Additionally, vis' buttons are rendered only when a visualization is selected.

For exporting MapVis I need to wrap the export in useEffect to make it work, rather than calling the exporting function directly.