Previously the _NET_WM_ICON would use the .ico which was also used for
the Windows icon. This icon used the dimensions 256x256, but the maximum
supported image size is 192x192, so a new image with the dimensions
64x64 has been added.
Since we know the image format anyways, the `image` dependency could
also be easily replaced with `png`, which cuts out a few extra unused
dependencies.
Christian Duerr