Mail icon for email lists in typeahead

Summary:
Adds a mail icon to use in the typeahead

Also, can we add a special class per obj-type? (May want to special color projects, etc) Will try to live without them.

Test Plan: photoshop

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D8259