Add --install-virtio option in snf-mkimage

If this is enabled, the program will try to install the specified VirtIO
drivers to the image.
Add a wizard page for the VirtIO drivers

Add a page in the dialog wizard that displays the current state of
the VirtIO drivers of the image and allow the user to update the
installed VirtIO drivers. This page will only be shown if the media
hosts a Windows image.