[x] add a command + click listener for non-sequential image selection
[ ] show context menu on right click if row isn't already selected? Finder does this and sets the item in some kind of semi-selected state. More applicable for acting on single images rather than groups.
[ ] update focused image to the very last one in selected image list? It's a bit odd to increment the focus index after selecting a bunch of images and performing some action on them because it will increment to the 2nd selected image.
See: https://github.com/tnc-ca-geo/animl-frontend/issues/25