GRP-15: Use a group for task assignments within a staff tool

Executive Summary: 
An XSEDE staff member needs to assign a task in a staff tool to a group (as opposed to an individual).
User Importance Summary: 
XSEDE community members need to be able to define arbitrary groups of people to which they can refer throughout the XSEDE system for authorization and communication purposes. The XSEDE staff and its myriad tasks are organized and planned in reference to a complex WBS structure that is essentially a set of groups. The ability to reflect the XSEDE WBS in groups and use those groups in staff tools would be greatly beneficial to the staff and would eliminate a nontrivial amount of clerical labor (and clerical errors).
Target Communities and Sizes: 
XSEDE staff - 10 < N < 100