(bug #2856) Activate the duplicate patrons detection and check birthdate only if...

(bug #2856) Activate the duplicate patrons detection and check birthdate only if one is set

This patch activate the check of unique member, it was checked but not shown, and the member was added even if a duplicate was
detected.
It improve the duplicate detection, to check the birthdate only if it was specified in the form.
And fix an url of "Yes" link(if the borrower added IS the duplicate detected).

Signed-off-by: Galen Charlton <galen.charlton@liblime.com>