Amends rotation intervals

The comments in this file are already well documented; they serve little purpose
in-line in the file, and add extra overhead if the commands are ever changed.

The rotation interval has been changed to weekly; we keep a year's worth (52
weeks) of logs before logrotate rotates them. This was done for security
purposes.
Amend clamscan program

`clamscan` and `clamdscan` have subtle differences, it seems. The former is
meant to be run as one-off and in cron jobs; the latter is daemonized. The
former also processes the virus definitions each time it runs; the latter does
not.

`clamdscan` doesn't support the --exclude switch, whereas `clamscan` does. To
that end, the command has been changed to support `clamscan`, thereby allowing
us to exclude `lost+found` as we do not particularly care about data stored
within that folder.

Originally, it was thought that AppArmor was contributing to this issue.
AppArmor, by default, restricts the behaviour of the clamdscan executable, and
investigation using `aa-status` showed that AppArmor was holding clamdscan in
enforce mode. I amended AppArmor to put clamdscan in to complain mode, but after
further testing, including the changes in this commit, it was realised that
AppArmor was not to blame. As a result, the changes to AppArmor were reverted,
and have been removed from the history of this branch as they serve no purpose.