Bug 15409 - Plugins section missing from Admin menu sidebar

 Bug 15409 - Plugins section missing from Admin menu sidebar

The sidebar menu in the Admin area of Koha is missing a section for
Plugins.

Test Plan:
1) Apply this patch
2) Log in with a user that has plugin permissions
3) Browse to a page with the admin menu sidebar, such as
   /cgi-bin/koha/admin/transport-cost-matrix.pl
4) Note the new Plugins section with a link to manage plugins
5) Log in with a user that has no plugin permissions
6) Revisit the same page, note the Plugins section is no longer visible

Signed-off-by: Aleisha <aleishaamohia@hotmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>