Bug 15400: Display date of birth and age more consistantly

Bug 15400: Display date of birth and age more consistantly

Test plan:
0) Apply the patch
1) Go to all of these pages
    Patron detail
    Other patron pages - look on the left side (circ-menu)
    Patron search
    Guarantor search ( go to child patron -> edit -> in guarantor
        section click "Set to patron"
    Search through "Check out" (in the header)

2) Confirm that does show date of birth and date consistantly,
    try it on patrons with and without date of birth set to find
    possible reggressions

Signed-off-by: Aleisha Amohia <aleishaamohia@hotmail.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Séverine QUEUNE <severine.queune@bulac.fr>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Michal Denar <black23@gmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>