Make closed vs open objects in object graphs more obvious

Summary: Ref T4788. It's not easy to tell at a glance which objects are open vs closed. Try to make that a bit more clear. This could probably use some more tweaking.

Test Plan:

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4788

Differential Revision: https://secure.phabricator.com/D16219