updated users_controller to use perms constants
updated users_controller to use perms constants

CDLUC3/dmptool,briri/roadmap,CDLUC3/roadmap,DigitalCurationCentre/roadmap,briri/roadmap,DMPRoadmap/roadmap,DMPRoadmap/roadmap,CDLUC3/dmptool,CDLUC3/dmptool,CDLUC3/roadmap,DigitalCurationCentre/roadmap,DMPRoadmap/roadmap,briri/roadmap,CDLUC3/roadmap,CDLUC3/roadmap,CDLUC3/dmptool,DigitalCurationCentre/roadmap