Bug 9988: Add the cronjob and print an upgrade message

Bug 9988: Add the cronjob and print an upgrade message

The Debian cron file and the misc crontab example are updated.
A message is printed when upgrading.

Note: At this moment the merge cron job is run once a day. This is imo a
good starting point. The load for this job greatly depends on the value of
pref AuthorityMergeLimit. Of course you can schedule the job more often,
and if this need is felt more globally, we can adjust it later.

Test plan:
[1] Run the dbrev and see the message.
[2] Read the changes to the cron files.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jacek Ablewicz <abl@biblos.pk.edu.pl>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>