Implement a "Project Members" object policy rule
I really dislike how the "hint" code works, but we almost never need to use it and the badness feels fairly well-contained.
Also pick up a quick feedback fix from D14863.
- Added test coverage, got it to pass.
- Created a project with "Visible To: Project Members".
Reviewers: joshuaspence, chad
Reviewed By: chad
Maniphest Tasks: T9019
Differential Revision: https://secure.phabricator.com/D14869