GRP-16: Use a group for email distribution

Executive Summary: 
A community member needs to use a group as the source for the members of an email distribution list. One notable reason for this is to avoid membership “drift” (changes over time) between a group used for access control and the corresponding email distribution list. E.g., XSEDE’s project management staff maintain groups for XSEDE project WBS areas. For each WBS area, they’d like a single group to be used both for access control on staff tools and for email communications.
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 email distribution list is a common type of group that's used heavily both within the XSEDE staff and throughout the research community XSEDE serves. Using a separate system for managing email vs. access control is unnecessarily laborious and error-prone.
Target Communities and Sizes: 
XSEDE staff - 10 < N < 100 XSEDE users - 10,000 < N < 100,000