Bug 25624: Add --where option to update_patrons_category.pl

Bug 25624: Add --where option to update_patrons_category.pl

The script did not allow to find empty fields or use wildcards

With this new option we will now have the ability to filter patrons by
some of their attributes.

Test plan:
1 - Run the script with no parameters and verify the help explains the parameters
2 - Try the script with one or more --where parameters, like:
  --where "firstname='koha'"
3 - Test null values
  --where "firstname IS NULL"
4 - Test like values with wildcards
  --where "firstname LIKE '%a%'
5 - Test like with the word null to find fields containing the word rather than being unset

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