Update PholioMockView Styles.

Summary: Less janky sidebar, new 'photoshop-like' texture for image background.

Test Plan: Tested mocks with and without side comments, hover over marked squares. Tested small and large images.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5216