Rename small symbolic app icons appropriately

App icons that use a symbolic style for their smaller sizes must use the -symbolic suffix for those sizes. If they don't, the symbolic versions will undesirably be used instead of the full-color ones in places where small icons are used and we'd expect to see a scaled-down version of the full-color icon, rather than a symbolic one.

When an app does want a symbolic version of any of these icons, it must ask for the icon name with -symbolic appended.