Draw 2 Rectangles below mount points to represent a disk capacity bar

Draws overtop text that's goes below the baseline like a 'j'. It's
fairly difficult to add extra space below the text as the places view
is a "details" view, so the text is vertically centered in the
widget's "row" as you'd desire it to in the main file view.

We can make the widget 8px taller, adding 4px above and below so
there's adequate room for the capacitybar, but that wastes 4px for
each mount point.

Ideally we'd use the "compact" view, which displays the text/size in a
column beside the icon. However the compact view was not designed to
take up the entire width of the viewport. It's also designed to
overflow with a horizontal scrollbar.