Screensaver defaults

[Harald Sitter]

https://bugs.edge.launchpad.net/ubuntu/+source/kubuntu-meta/+bug/273667

IMHO we should ship a couple of savers by default (and possibly hook
update-notifier in the KCM, so it recommends installing some other
fancy packages), but stick to no-by-default. The reason for
no-by-default is stated in my bug comment.

Also, we probably ought to test kscreensaver before that, last I
checked it had grave issues with GL savers.