allow sub-admin not to change the category (fixes #3072)
allow sub-admin not to change the category (fixes #3072)

C-nakajima/OpenPNE3,ShinichiU/OpenPNE3,upsilon/travis-test,ShinichiU/OpenPNE3,isaosano/OpenPNE3,kashiwasan/symfony-advanced,kashiwasan/symfony-advanced,C-nakajima/OpenPNE3,nishizoe/OpenPNE3,ShinichiU/OpenPNE3,C-nakajima/OpenPNE3,upsilon/travis-test,nishizoe/OpenPNE3,isaosano/OpenPNE3,isaosano/OpenPNE3,ShinichiU/OpenPNE3,isaosano/OpenPNE3,C-nakajima/OpenPNE3