Make projects policy-aware

Summary: We managed to move enough Owners stuff aside to make this reasonable; make projects implement the policy interface and projectquery use cursor-based paging.

Test Plan:

• Grepped for ProjectQuery callsites.
• Created an audit comment.
• Used project.query to query projects.
• Loaded homepage.
• Viewed Maniphest task list, grouped by project.
• Viewed project list.
• Created / edited project.
• Browsed Owners.

Reviewers: vrana, btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T603

Differential Revision: https://secure.phabricator.com/D3200