Bug 18375: Better readability of patron category table for zero ages and fees

Bug 18375: Better readability of patron category table for zero ages and fees

In patron category table, this patch displays zero / empty values for ages and
fees with '-' for better readability

To test:
- Go to Home > Administration > Patron categories
- Verify that you have 0 years and/or only years in Age required and Uper age limit colums
- Verify that you have Enrollment and Hold fees of 0.00
- Apply patch
- Verify that such values are replaced by - to enhance table readability

Signed-off-by: Luke Honiss <luke.honiss@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>