Bug 6506: Followup add warning in the system information tab.

Bug 6506: Followup add warning in the system information tab.

Add a warning in the system information tab of the about page.

Test plan:
Set OPACPrivacy = 1 and AnonymousPatron = 0 and go on the about page,
tab 'system information'. Check that the warning appears.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Mason James <mtj@kohaaloha.com>
http://bugs.koha-community.org/show_bug.cgi?id=6509
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>
(cherry picked from commit 4c709c600799392eae67f715cff1b5a2e574c042)

Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>