Bug 28859: Correctly handle 'Checked out by' visibility

Bug 28859: Correctly handle 'Checked out by' visibility

We must have the column in the table and let DT deal with the
visibility.

This patch hides the "Checked out by" column by default if
RecordStaffUserOnCheckout is off, but the DT column settings is aware of
its existence and the end user can still display the column.

IMO that's the most optimal situation considering both maintenance and ergonomic.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>