metapackages are expanded into a list of its dependencies.
This achieves two goals:
- the installer shows which packages will be installed
  together with the metapackage
- after deleting meta package, apt-get autoremove not
  will remove its immediate dependencies

Not much use, and spoils postinstall.d messages with
FAILED (to mount the already-mounted flash drive).

See-also: 96f1d069c

This commit is actually a rework of what's been done
in RELENG-e2k-workstation private branch (along with
a few more generic fixups).

New version of alterator-auth uses sssd.

Nextcloud provides more functionality as free software
being a developer-led fork of ownCloud.

...and uncomment all network services such as
Moodle, Mediawiki, Owncloud, Rujel.

- Use firefox-esr instead of firefox
- Use mariadb insead of MySQL
- Add memtest check to disk menu
- Use kde5 without kde5-kdepim
- Use Moodle 2.5 instead of 2.2