Tighten up CSS on object-list a bit.

Summary:

• Fix unintended round edges.
• Reduce height 4px;
• Align title and date
• Fix mobile/tablet spacing

Test Plan: Photoshop, UIExamples, Config, Paste, Maniphests (all mobile and desktop views)

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5445