Fix "fullName" rules for Maniphest transaction email

Summary: I changed this from getName to getFullName to make attached revisions, etc., render with "Dnnn", but accidentally made all users render as "username (Full Name)". Be a little more surgical in application of full names.

Test Plan: Created a task and attached a CC, a task and a revision. Verified the task and revision rendered with "Tnn", "Dnn" but the CC rendered as "username".

Reviewers: btrahan, vrana

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D3041