Tighten up object list 2px

Summary: Pulls in the top 2px and left 2px. Also reduces to 13px as standard. The 14px never looked decent to me. Main objective here is to have it feel more table-like instead of a sea of white space.

Test Plan: Tested layouts in Maniphest, Config, and UIExamples.

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5551