Make "user role" editing more clear

Summary: The various interfaces here are in conflict about what a role is and isn't. Make them all consistent.

Test Plan: Edited some users into various roles, verified they reported correctly.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1190

Differential Revision: https://secure.phabricator.com/D2415