R1:fcaf56332fad

Use parameterized datasources for Maniphest authors and subscribers

Summary: Ref T4100. Update these controls to allow functions like `viewer()`.

Test Plan: Used the new controls.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4100

Differential Revision: https://secure.phabricator.com/D12527