De-garbage the horrible garbage project section of the policy selection control

Summary:
Fixes T4136.

When listing projects in the "Visible To" selector control:

• Instead of showing every project you are a member of, show only a few.
• Add an option to choose something else which isn't in the menu.
• If you've used the control before, show the stuff you've selected in the recent past.
• If you haven't used the control before or haven't used it much, show the stuff you've picked and them some filler.
• Don't offer milestones.
• Also don't offer milestones in the custom policy UI.

Test Plan:

• Selected a project.
• Used "find" to select a different project.
• Saw reasonable defaults.
• Saw favorites stick.
• Tried to typeahead a milestone (nope).
• Used "Custom Policy", tried to typeahead a milestone (nope).
• Used "Custom Policy" in general.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4136

Differential Revision: https://secure.phabricator.com/D15184