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., a project maintains groups for project WBS areas. For each WBS area, they’d like a single group to be used both for access control in project applications and for email communications.
User Importance Summary: 
Community members need to be able to define arbitrary groups of people to which they can refer authorization and communication purposes. The email distribution list is a common type of group that's used heavily in the public research computing community. Using a separate system for managing email vs. access control is unnecessarily laborious and error-prone.
Target Communities and Sizes: 
Community members - 10,000 < N < 100,000