Remove anacron data from system plug-in

The system plug-in is a dumping ground of all sorts of random
bits and pieces. Move the anacron stuff to its own file.
Remove user crontabs from crontab plug-in

It's unwise to collect user crontabs (especially "for all accounts
with a directory in /home"..) since they could contain
confidential information. The icky shell call-out also has not
worked in some time - remove it all.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>
Remove cron related information from system plug-in

The cron data does not belong in the system plug-in and it seems
pointless to have a separate module just for crontabs (but not
for cron!). Move the cron logs and tabs into a new plug-in named
cron.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>