profiles/kde: pkglist: update.
stage-pool/mnt-system-copy@.sh: semi-fix to get at least a working /mnt/system repo on the destination.

It will still have origin pointing to the installation framework's checkout and
not to the upstream, but well...
configs-sergey: add a set of configs.
configs-*/dest: update, adding 'kde' and 'virtualbox' profiles where appropriate.
functions.sh: add experimental support for per-profile config directories.

As of now, they have the highest priority.
profiles/uefi: add a profile containing configs for the ESP partition and use it where needed.

...instead of ad-hoc 'configs-*/filesystems' file in each config set.
profiles/virtualbox: split off 'vboxusers' group addition into the respective profile.

Thus configs which do not make use of 'virtualbox' profile will not fail at user
creation stage due to inexistent group.