This allows us to show the devices in a GUI with a nice icon. Some of the icon
mappings are not perfect and I'll be asking the GNOME designers for some
additions to the icon specification.
Custom vendor icons can also be specified, and /usr/share/fwupd/icons would be
a good place to put them. If vendor icons are used they should show a physical
device with the branding, rather than just the vendor logo.