added assign_user_groups permission key to fix error on assign group to user dialog
added assign_user_groups permission key to fix error on assign group to user dialog

TimDix/concrete5,avdevs/concrete5,matt9mg/concrete5,matt9mg/concrete5,matt9mg/concrete5,TimDix/concrete5,MichaelMaar/concrete5,TimDix/concrete5,MichaelMaar/concrete5,MichaelMaar/concrete5,avdevs/concrete5,avdevs/concrete5