Minor spacing on object-list-items

Summary: Ran into a few edge cases under 'Needs Triage', this adds a bit more space under unassigned tasks with projects.

Test Plan: Test Maniphest, Needs Triage, Homepage, and UI Examples.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5452