Update ObjectItemView to a 4px grid

Summary: Cleaning up the spacing on ObjectItemView to be on a 4px grid and a little more consistent.

Test Plan: Review changes on a grid in Photoshop

Reviewers: epriestley, btrahan

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D6088