Bug 19454: Add -category parameter to borrowers-force-messaging-defaults.pl

Bug 19454: Add -category parameter to borrowers-force-messaging-defaults.pl

Instead of updating patrons over all patron categories, it would be
helpful if we could filter on a specified category.

Test plan:
[1] Select two patrons A and B in say categories C1 and C2.
[2] Change the msg prefs for A and B away from defaults.
[3] Run borrowers-force-messaging-defaults.pl -doit -cat C1
    Verify that patron A changed and patron B did not.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Charles Farmer <charles.farmer@inLibro.com>

Amended: Replace -category by --category. (marcelr 20180314)

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>