Closes#2265
There's also new code for showing a different icon for snapshots, files,
and DOI/URL links, like the web library and iOS app, but it's commented
out for now. The bitmap icons create too much visual noise with the
greater information density and hierarchical tree of the desktop app
(not to mention many more low-DPI displays). We can revisit after
switching to SVGs across the board.
b0ba7e4646