Show primary email in approval queue interface

Summary:
Request from @csilvers. When approving users, the primary email address is useful for administrators.

(This queue is only accessible by administrators, so this doesn't expose email information in general.)

Test Plan:

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: shadowhand, csilvers, epriestley

Differential Revision: https://secure.phabricator.com/D8589