Tighten CSS spacing in PHUIObjectListViewy

Summary: Who doesn't like tighter CSS! Evens up the spacing top and bottom when in a phui-object-box

Test Plan: External Accounts.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: Korvin, epriestley, aran

Differential Revision: https://secure.phabricator.com/D7948