Split users apart from projects/packages in reviewer and audit UIs

Summary: Ref T1279. Show separate sections for "Reviewers" and "Project Reviewers" (Differential) and for "Auditors" and "Package/Project Auditors" (Diffusion/Audit).

Test Plan:

• Looked at a commit. Saw separation.
• Looked at a revision. Saw separation.

Reviewers: chad, btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T1279

Differential Revision: https://secure.phabricator.com/D7233