Have DifferentialRevisionListView return ObjectBoxView

Summary: Uses PHUIObjectBoxView to display lists of diffs in Differential and Diffusion, unless embedded on a dashboard.

Test Plan:
Test Dashboard panel, Differential home, Commit, and Diff

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11659