Don't show description box in Pholio when there isnt one

Summary: n/a

Test Plan: Added title and description to 1 of 2 mocks, toggled left and right, saw correct CSS.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9580