Bug 14763: Calculate and display patron age

 Bug 14763: Calculate and display patron age

To test:
1) Go to patron Details page (ie http://localhost:8081/cgi-bin/koha/members/moremember.pl?borrowernumber=51)
2) Confirm that '(x years)' is showing next to the Date of Birth and is correct according to DOB (ie if DOB: 30/11/1996, Age: 19 years)
3) Edit date of birth to be a month later (ie from 30 November to 30 December) so that, as of the date you are testing, the patron has not had their birthday yet
4) Confirm that age changes to be one year younger
5) Edit date of birth to be a different year
6) Confirm that age changes accordingly

Works as expected.
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>