Cleaning http_proxy and ftp_proxy settings in chroot, people using apt proxies set them throught the apt pseudo-proxy options, and people using real proxies use config/environment.{chroot,binary} to set them.

Adding --system option to define the resulting image type to be a live system or a normal, non-live system.

This is the first step in conglomerating code for all hdd-ish
image types, independent of the partitioning scheme being used,
and adding future hdd-ish image types for virtualiziation software.

Adding support for ext4 for binary and chroot filesystem, including partial patch from Ben Howard <ben.howard@canonical.com> (Closes: #639298).

Adding kubuntu mode in order to have different defadefault hooks enabled for ubuntu and kubuntu (needed for #630088).