Add View, Edit and Join policies to PhabricatorProject

Summary:

• In ProjectQuery, always load the viewer's membership in the project because we need it to perform a CAN_VIEW test.
• Add storage for the view, edit and join policies.
• A user can always view a project if they are a member.
• A user can always join a project if they can edit it.
• Editing a project requires both "view" and "edit" permissions, and edit does not imply view.
• This has no effect on the application yet.

Test Plan: See next diff.

Reviewers: vrana, btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T603

Differential Revision: https://secure.phabricator.com/D3219