stage-pool/dest-install-fstab@.sh: improve device name generation logic, explicitly use label and UUID when possible.
profiles, configs: add 'internal' profile with packages required by the installer itself.
profiles: split off 'splash' profile.

It is incomplete currently (does not install required packages).
system: update checkout.

Submodule system 939365a..fea1a6f:
> user/artwork: get rid of kde-dependent modules (statically merged into user-
skel).
> configs: partially get rid of pool; split off a 'virtualbox' profile.
profiles: virtualbox: install 'virtualbox' set of configs.