Bug 13998: Reintroduce use of Koha::Database for C4::Ratings

Bug 13998: Reintroduce use of Koha::Database for C4::Ratings

It has been removed by bug 13852, because before bug 13852,
Koha::Database was used in C4:Members which was used by
C4::VirtualShelves which was used by C4::Auth which was finally used by
C4::Ratings...

Test plan:
At the opac, record detail page, note the record using the stars.
Without this patch it does not work.

Signed-off-by: Nick Clemens <nick@quecheelibrary.org>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
http://bugs.koha-community.org/show_bug.cgi?id=12998
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>