Bug 24549: Do not set "last patron" cookie if showLastPatron is disabled

Bug 24549: Do not set "last patron" cookie if showLastPatron is disabled

If the showLastPatron syspref is disabled, we should not store the 3
cookies we use for this feature.

Test plan:
0/ Do not apply this patch
1/ Turn off showLastPatron
2/ Search for a patron, click on a result
3/ Open the cookie list of your browser
=> You see 3 cookies named lastborrowercard, lastborrowername,
lastborrowernumber
4/ Remove them
5/ Apply the patch
6/ Reload the patron detail page
=> The 3 cookies are not created
7/ Turn the pref on
8/ Reload the patron detail page
=> The 3 cookies are created
9/ Eat one of them.

QA note: it's a bit dirty, we should do that JS side, but
staff-global.js is too widely used to make the change easy. Any other
suggestions welcomed.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>