Add data directory
Improve desktop entry
Import preunpackfs module

preunpackfs mounts an image to a mount point where unpackfs will find the
real rootfs image.

This is an extra step required by LiveOS images (see [1]) which have
a squashfs file that contains a ext4 rootfs image.

[1] http://fedoraproject.org/wiki/LiveOS_image
Add extlinux module