Mediawiki and Nextcloud take a long time to set up
on the 1st boot of the system.
They are removed by default.
The user who wants to install them
will be warned about the long 1st boot.

These have been:
- taken from x86_64 server iso (in substituted form);
- checked against m-p-d where needed;
- renamed from centaurus-* to centaurus/*;
- updated with s/samba-server/samba/;
- archdep bits adjusted for m-p-d/m-p syntax difference;
- amended with some tester feedback based additions included;
- pruned regarding p9/branch packages availability.